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<chapter id="encoding-guide">
<title>Kodowanie przy użyciu <application>MEncodera</application></title>

<sect1 id="menc-feat-dvd-mpeg4">
<title>Rippowanie DVD do wysokiej jakości pliku MPEG-4 ("DivX")</title>

<para>
  Jednym z często zadawanych pytań jest "Jak zrobić rip najlepszej jakości
  przy danej objętości?". Innym pytaniem jest "Jak zrobić najlepszy możliwy
  rip? Nie ważne jaka będzie objętość, chcę najlepszej jakości."
</para>

<para>
  To drugie pytanie jest przynajmniej źle postawione. W końcu, jeśli nie
  przejmujesz się wielkością pliku, mógłbyć po prostu skopiować strumień
  MPEG-2 z DVD. Pewnie, dostaniesz AVI wielkości około 5GB, ale jeśli chcesz
  najlepszej jakości i nie przejmujesz się wielkością to jest to najlepsze
  wyjście.
</para>

<para>
  Tak na prawdę, powodem dla którego chcesz przekodować DVD na MPEG-4 jest to,
  że <emphasis role="bold">przejmujesz</emphasis> się wielkością pliku.
</para>

<para>
  Ciężko jest pokazać książkowy przepis na tworzenie ripu DVD bardzo wysokiej
  jakości. Trzeba wziąć pod uwagę kilka czynników, i powinieneś rozumieć
  szczegóły albo masz dużą szansę że nie będziesz zadowolony z wyników.
  Poniżej zbadamy niektóre problemy i pokażemy przykład. Zakładamy że używasz
  <systemitem class="library">libavcodec</systemitem> do kodowania obrazu,
  chociaż ta sama teoria działą też przy innych kodekach.
</para>

<para>
  Jeśli to wydaje Ci się za dużo, to pewnie powinieneś użyć jednej z wielu
  nakładek dostępnych w
  <ulink url="http://mplayerhq.hu/homepage/design7/projects.html#mencoder_frontends">sekcji MEncodera</ulink>
  naszej strony z powiązanymi projektami.
  W ten sposób, powinno się udać otrzymać ripy wysokiej jakości bez zbyt
  myślenia za dużo, ponieważ te narzędzia są projektowane by podejmować za
  Ciebie mądre decyzje.
</para>

<sect2 id="menc-feat-dvd-mpeg4-preparing-encode">
<title>Przygotowanie do kodowania: Identyfikowanie materiału źródłowego
i framerate</title>
<para>
  Zanim w ogóle zaczniesz myśleć o kodowaniu filmu, musisz podjąć kilka
  początkowych kroków.
</para>

<para>
  Pierwszym i najważniejszym krokiem przed kodowaniem powinno być
  ustalenie jakim typem filmu się zajmujesz.
  Jeśli Twój film jest z DVD albo telewizji (zwykłej, kablowej czy
  satelitarnej), będzie w jednym z dwóch formatów: NTSC w Ameryce Północnej
  i Japonii, PAL w Europie itp.
  Trzeba sobie jednak zdawać sprawę z tego, że jest to tylko format do
  prezentacji w telewizji, i często <emphasis role="bold">ne</emphasis> jest
  oryginalnym formatem filmu.
  Doświadczenie pokazuje że filmy NTSC są trudniejsze do kodowania, ponieważ
  jest więcej elementów do zidentyfikowania w źródle.
  Żeby zrobić odpowienie kodowanie musisz znać oryginalny format filmu.
  Nieuwzględnienie tego skutkuje wieloma wadami wynikowego pliku, na przykład
  brzydkie artefakty przeplotu i powtórzone albo zagubione klatki.
  Poza tym że są pbrzydkie, artefakty są też szkodliwe dla kodowania:
  Dostaniesz gorszą jakość na jednostkę bitrate.
</para>

<sect3 id="menc-feat-dvd-mpeg4-preparing-encode-fps">
<title>Ustalanie źródłowego framerate</title>
<para>
  Poniżej jest lista popularnych typów materiału źródłowego, gdzie można je
  najczęściej znaleźć i ich własności:
</para>
<itemizedlist>
<listitem><para>
  <emphasis role="bold">Typowy film</emphasis>: Tworzony do wyświetlania przy
  24fps.
</para></listitem>
<listitem><para>
  <emphasis role="bold">Film PAL</emphasis>: Nagrywany kamerą video PAL
  z prędkością 50 pól na sekundę.
  Pole składa się tylko z parzystych albo nieparzystych linii klatki.
  Telewizja była projektowana by odświerzać je naprzemiennie, jako tania forma
  analogowej kompresji.
  Ludzkie oko podobno kompensuje ten efekt, ale jeśli zrozumiesz przeplot
  nauczysz się go widzieć też w telewizji i nigdy już nie będziesz z niej
  zadowolony.
  Dwa pola <emphasis role="bold">nie</emphasis> dają pełnej klatki, ponieważ
  są uchwycone co 1/50 sekundy, więc nie pasują do siebie, chyba że nie ma
  ruchu.
</para></listitem>
<listitem><para>
  <emphasis role="bold">Film NTSC</emphasis>: Nagrany kamerą NTSC z prędkością
  6000/1001 pól na sekundę, albo 60 pól na sekundę w erze przedkolorowej.
  Poza tym podobny do PAL.
</para></listitem>
<listitem><para>
  <emphasis role="bold">Animacja</emphasis>: Zazwyczaj rysowana przy 24fps,
  ale zdarzają się też z mieszanym framerate.
</para></listitem>
<listitem><para>
  <emphasis role="bold">Grafika komputerowa (CG)</emphasis>: Może być dowolny
  framerate, ale niektóre są częstsze niż inne; wartości 24 i 30 klatek na
  sekundę są typowe dla NTSC, a 25fps jest typowe dla PAL. 
</para></listitem>
<listitem><para>
  <emphasis role="bold">Stary film</emphasis>: Rozmaite niższe framerate.
</para></listitem>
</itemizedlist>
</sect3>

<sect3 id="menc-feat-dvd-mpeg4-preparing-encode-material">
<title>Identyfikowanie materiału źródłowego</title>
<para>
  Filmy składające się z klatek nazywa się progresywnymi,
  podczas gdy te składające się z niezależnych pól nazywa się
  z przeplotem, albo filmem - chociaż ten drugi termin jest niejasny.
</para>
<para>
  Żeby nie było za łatwo, niektóre filmy są kombinacją kilku powyższych typów.
</para>
<para>
  Najważniejszą różnicą między tymi formatami, jest to że niektóre są oparte
  na klatkach a inne na polach.
  <emphasis role="bold">Zawsze</emphasis> gdy film jest przygotowywany do
  wyświetlania w telewizji jest przekształcany na format oparty na polach.
  Rozliczne metody którymi się tego dokonuje są wspólnie nazywane "pulldown",
  a niesławne "3:2 telecine" z NTSC jest jednym z jego rodzajów.
  Jeżeli oryginał nie był też oparty na polach (z tą samą prędkością),
  dostajesz film w innym formacie niż oryginał.
</para>

<itemizedlist>
<title>Jest kilka popularnych typów pulldown:</title>
<listitem><para>
  <emphasis role="bold">pulldown PAL 2:2</emphasis>: Najprzyjemniejszy z nich
  wszystkich.
  Każda klatka jest pokazywana przez czas dwóch pól, poprzez wydobycie
  parzystych i nieparzystych linii i pokazywanie ich na przemian.
  Jeśli oryginalny materiał miał 24fps, ten proces przyspiesza film o 4%.
</para></listitem>
<listitem><para>
  <emphasis role="bold">pulldown PAL 2:2:2:2:2:2:2:2:2:2:2:3</emphasis>:
  Każda 12ta klatka jest pokazywana przez czas trzech pól zamiast tylko dwóch.
  Dzięki temu nie ma przyspieszenia o 4%, ale proces jest o wiele trudniejszy
  do odtworzenia.
  Zazwyczaj występuje w produkcjach muzycznych, gdzie zmiana prędkości o 4%
  poważnie by uszkodziła muzykę.
</para></listitem>
<listitem><para>
  <emphasis role="bold">NTSC 3:2 telecine</emphasis>: Klatki są pokazywane na
  przemian przez czas 3ch albo 2ch pól.
  To daje częstotliwość pól 2.5 raza większą niż oryginalna częstotliwość
  klatek. Rezultat jest też lekko zwolniony z 60 pól na sekundę do 60000/1001
  pól na sekundę by utrzymać częstotliwość pól w NTSC.
</para></listitem>
<listitem><para>
  <emphasis role="bold">NTSC 2:2 pulldown</emphasis>: Używane do pokazywania
  materiałów 30fps na NTSC.
  Przyjemne, dokładnie jak pulldown 2:2 PAL.
</para></listitem>
</itemizedlist>

<para>
  Są też metody konwersji między filmami PAL i NTSC, ale ten temat
  wykracza poza zakres tego podręcznika.
  Jeśli natkniesz się na taki film, i chcesz go zakodować, to największe
  szanse masz odnajdując kopię w oryginalnym formacie.
  Konwersja między tymi dwoma formatami jest wysoce destrukcyjna i nie może
  zostać czysto odwrócona, więc kodowanie będzie o wiele gorszej jakości jeśli
  jest robione z przekonwertowanego źródła.
</para>
<para>
  Gdy film jest zapisywany na DVD, kolejne pary pól są zapisywane jako klatka,
  pomimo tego że nie są przezaczone do wyświetlania razem.
  Standard MPEG-2 używany na DVD i w cyfrowej TV pozwala na zakodowanie
  oryginalnej progresywnej klatki i na przechowanie w nagłówku klatki ilości
  pól przez które ta klatka powinna być pokazana.
  Filmy zrobione przy użyciu tej metody są często określane mianem "miękkiego
  telecine" (soft-telecine), ponieważ proces ten tylko informuje odtwarzacz że
  ma on zastosować pulldown, a nie stosuje go samemu.
  Tak jest o wiele lepiej, ponieważ może to zostać łatwo odwrócone (a tak na
  prawdę zignorowane) przez koder i ponieważ zachowuje możliwie najwyższą
  jakość.
  Niestety, wielu producentów DVD i stacji nadawczych nie stosuje prawidłowych
  technik kodowania ale w zamian produkuje filmy przy użyciu "twardego
  telecine" (hard-telecine), gdzie pola są faktycznie powtórzone
  w zakodowanym MPEG-2.
</para>
<para>
  Procedury radzenia sobie z takimi przypadkami będą omówione
  <link linkend="menc-feat-telecine">w dalszej części przewodnika</link>.
  Teraz podamy tylko kilka wskazówek jak identyfikować z jakim typem materiału
  mamy do czynienia.
</para>

<itemizedlist>
<title>Regiony NTSC:</title>
<listitem><para>
  Jeśli <application>MPlayer</application> wyświetla w trakcie oglądania filmu
  że framerate zostało zmienione na 24000/1001, i nigdy nie powraca, to jest
  to prawie na pewno progresywny materiał na którym zastosowano "miękkie
  telecine".
</para></listitem>
<listitem><para>
  Jeśli <application>MPlayer</application> pokazuje że framerate zmienia się
  między 24000/1001 i 30000/1001 i czasami widzisz "grzebienie" to jest kilka
  możliwości.
  <!-- Torinthiel: grzebienie mi najlepiej pasują, ale może jest oficjalne tłumaczenie -->
  Kawałki 24000/1001fps są prawie na pewno progresywne, poddane "miękkiemu
  telecine", ale fragmenty  30000/1001 fps mogą albo być 24000/1001 poddanym
  "twardemu telecine" albo filmem NTCS o 60000/1001 polach na sekundę.
  Używaj tych samych metod co w następnych dwóch przypadkach żeby je odróżnić.
</para></listitem>
<listitem><para>
  Jeśli <application>MPlayer</application> nigdy nie pokazuje informacji
  o zmianie framerate i każda klatka z ruchem wygląda jak grzebień, to masz
  film NTSC z 60000/1001 polami na sekundę.
</para></listitem>
<listitem><para>
  Jeśli <application>MPlayer</application> nigdy nie pokazuje informacji
  o zmianie framerate i dwie klatki z każdych pięciu mają grzebienie, to film
  jest 24000/1001 fps poddanym "twardemu telecine".
</para></listitem>
</itemizedlist>

<itemizedlist>
<title>Regiony PAL:</title>
<listitem><para>
  Jeśli nie widzisz grzebieni, to jest to 2:2 pulldown.
</para></listitem>
<listitem><para>
  Jeśli na przemian przez pół sekundy widzisz grzebienie a potem nie, to masz
  2:2:2:2:2:2:2:2:2:2:2:3 pulldown.
</para></listitem>
<listitem><para>
  Jeśli zawsze widzisz grzebienie w trakcie ruchu, to film jest filmem PAL
  wyświetlanym z 50 polami na sekundę.
  <!-- Torinthiel: wyświetlanym czy nagranym? -->
</para></listitem>
</itemizedlist>

<note><title>Podpowiedź:</title>
<para>
  <application>MPlayer</application> może zwolnić odtwarzanie filmu opcją
  -speed albo odtwarzać klatka po klatce.
  Spróbuj użyć opcji <option>-speed</option> 0.2 żeby oglądać film bardzo
  wolno, albo naciskaj wielokrotnie klawisz "<keycap>.</keycap>" żeby
  wyświetlać jedną klatkę na raz. Może to pomóc zidentyfikować wzorzec jeśli
  nie możesz go dostrzec przy pełnej prędkości.
</para>
</note>
</sect3>
</sect2>

<sect2 id="menc-feat-dvd-mpeg4-2pass">
<title>Stały kwantyzator a tryb wieloprzebiegowy</title>

<para>
  Jest możliwe zakodowanie filmu z szeroką gamą jakości.
  Z nowoczesnymi koderami i odrobiną kompresji przed kodekiem (zmniejszenie
  rozdzielczości i usuwanie szumu), możliwe jest osiągnięcie bardzo dobrej
  jakości przy 700 MB, dla 90-110 minutowego filmu kinowego.
  Dodatkowo tylko najdłuższe filmy nie dają się zakodować na 1400 MB z prawie
  doskonałą jakością.
</para>

<para>
  Są trzy podejścia do kodowania video: stały bitrate (CBR),
  stały kwantyzator i tryb wieloprzebiegowy (ABR, uśrednione bitrate).
</para>

<para>
  Złożoność klatek filmu, a zatem i ilość bitów potrzebna na ich zakodowanie,
  może się bardzo mocno zmieniać w zależności od sceny.
  Nowoczesne kodery potrafią się dostosowywać do tych zmian i zmieniać
  bitrate.
  Jednak w prostych trybach, takich jak CBR, kodery nie znają zapotrzebowania
  na bitrate w przyszłych scenach, więc nie mogą na długo przekraczać
  wymaganego bitrate.
  Bardziej zaawansowane tryby, takie jak kodowanie wieloprzebiegowe, potrafią
  wziąć pod uwagę statystyki z poprzednich przebiegów; to naprawia wyżej
  wymieniony problem.
</para>

<note><title>Uwaga:</title>
<para>
  Większość kodeków obsługujących kodowanie ABR obsługuje tylko kodowanie
  dwuprzebiegowe, podczas gdy niektóre inne, na przykład
  <systemitem class="library">x264</systemitem> albo
  <systemitem class="library">XviD</systemitem> potrafią wykonywać wiele
  przebiegów, z lekką poprawą jakości po każdym przebiegu. Jednak ta poprawa
  nie jest zauważalna ani mierzalna po około 4tym przebiegu.
  Dlatego też, w tej części, tryb dwuprzebiegowy i wieloprzebiegowy będą
  używane zamiennie.
</para>
</note>

<para>
  W każdym z tych trybów, kodek video (na przykład
  <systemitem class="library">libavcodec</systemitem>)
  dzieli klatkę obrazu na makrobloki 16x16 pikseli i stosuje do każdego z nich
  kwantyzator. Im niższy kwantyzator, tym lepsza jakość i tym wyższe bitrate.
  Metody jakiej koder używa do ustalenia kwantyzatora są różne i można nimi
  sterować. (Jest to straszliwe uproszczenie, ale wystarcza do zrozumienia
  podstaw.)
</para>

<para>
  Kiedy podajesz stałe bitrate, kodek koduje usuwając tyle szczegółów ile musi
  i tak mało jak to tylko możliwe żeby pozostać poniżej podanego bitrate.
  Jeśli na prawdę nie obchodzi cię wielkość pliku, możesz użyć CBR i podać
  nieskończone bitrate (W praktyce oznacza to bitrate na tyle wysokie że nie
  stanowi bariery, na przykład 10000Kbit.) Bez żadnego ograniczenia na bitrate
  kodek użyje najniższego możliwego kwantyzatora do każdej klatki (ustalonego
  dla <systemitem class="library">libavcodec</systemitem> opcją
  <option>vqmin</option>, domyślnie 2).
  Gdy tylko podasz bitrate na tyle niskie że kodek musi używać wyższego
  kwantyzatora, to prawie na pewno niszczysz film.
  Żeby tego uniknąć, powinieneś pewnie zmniejszyć rozdzielczość filmu, metodą
  opisaną dalej.
  Ogólnie, jeśli troszczysz się o jakość, powinieneś unikać CBR.
</para>

<para>
  Przy stałym kwantyzatorze, kodek używa na każdym makrobloku tego samego
  kwantyzatora, podanego opcją <option>vqscale</option>
  (w przypadku <systemitem class="library">libavcodec</systemitem>).
  Jeśli chcesz możliwie najlepszy efekt, znów ignorując bitrate, możesz użyć
  <option>vqscale=2</option>. Da to ten sam bitrate i PSNR (peak
  signal-to-noise ratio, szczytowa proporcja sygnału do szumu) co CBR
  z <option>vbitrate</option>=nieskończoność i domyślnym
  <option>vqmin</option>.
</para>

<para>
  Problemem przy stałym kwantyzatorze jest to, że używa podanego kwantyzatora
  niezależnie od tego czy makroblok tego wymaga czy nie. To znaczy że można by
  było zastosować do makrobloku wyższy kwantyzator bez utraty postrzegalnej
  jakości. Dlaczego marnować bity na niepotrzebnie niski kwantyzator?
  Mikroprocesor ma tyle cykli ile jest czasu, ale jest tylko pewna ilość bitów
  na twardym dysku.
</para>

<para>
  Przy kodowaniu dwuprzebiegowym, pierwszy przebieg potraktuje film jak przu
  ustawieniu CBR, ale zachowa informacje o własnościach każdej klatki. Te dane
  są później używane przy drugim przebiegu do podejmowania słusznych decyzji
  o używanym kwantyzatorze. Przy szybkich scenach albo niewielu szczegółach
  pewnie użyje większego kwantyzatora, podczas gdy dla powolnych,
  szczegółowych scen będzie niższy kwantyzator.
</para>

<para>
  Jeśli używasz <option>vqscale=2</option> to marnujesz bity. Jeśli używasz
  <option>vqscale=3</option> to nie dostajesz najlepszej możliwej jakości.
  Załóżmy że zakodowałeś swoje DVD przy <option>vqscale=3</option>
  i dostałeś bitrate 1800Kbit. Jeśli zrobisz dwa przebiegi
  z <option>vbitrate=1800</option> ostateczny wynik będzie miał
  <emphasis role="bold">wyższą jakość</emphasis> przy
  <emphasis role="bold">tym samym bitrate</emphasis>.
</para>

<para>
  Ponieważ jesteś już przekonany że prawidłowym wyborem są dwa przebiegi,
  prawdziwym pytaniem jest jakiego bitrate użyć. Nie ma jednej odpowiedzi.
  Idealnie chcesz wybrać bitrate będący najbliżej równowagi między jakością
  a wielkością pliku. To się zmienia w zależności od filmu.
</para>

<para>
  Jeśli wielkość nie ma znaczenia, dobrym punktem wyjściowym do bardzo
  wysokiej jakości jest około 2000Kbit plus minus 200Kbit.
  Jeśli jest dużo akcji albo szczegółów, albo po prostu masz bardzo wrażliwe
  oko, możesz się zdecydować na 2400 albo 2600.
  Przy niektórych DVD możesz nie zauważyć różnicy przy 1400Kbit. Dobrym
  pomysłem jest poeksperymentowanie z kilkoma scenami i różnymi wartościami
  bitrate żeby nabrać wyczucia.
</para>

<para>
  Jeśli chcesz konkretnej wielkości, musisz jakoś obliczyć bitrare.
  Ale zanim to zrobisz, musisz wiedzieć ile miejsca potrzebujesz na dźwięk,
  więc powinieneś <link linkend="menc-feat-dvd-mpeg4-audio">ściągnąć go</link>
  najpierw.
  Możesz wyliczyć bitrate z następującego równania:
  <systemitem>bitrate = (wielkość_docelowa_w_MBajtach - wielkość_dźwięku_w_MB)
  * 1024 * 1024 / długość_w_sekundach * 8 / 1000</systemitem>
  Na przykład by wcisność dwugodzinny film na płytkę 702MB, z 60MB ścieżki
  dźwiękowej, bitrate video musi być:
  <systemitem>(702 - 60) * 1024 * 1024 / (120*60) * 8 / 1000
  = 740kbps</systemitem>
</para>

</sect2>


<sect2 id="menc-feat-dvd-mpeg4-constraints">
<title>Constraints for efficient encoding</title>

<para>
  Due to the nature of MPEG-type compression, there are various
  constraints you should follow for maximal quality.
  MPEG splits the video up into 16x16 squares called macroblocks,
  each composed of 4 8x8 blocks of luma (intensity) information and two
  half-resolution 8x8 chroma (color) blocks (one for red-cyan axis and
  the other for the blue-yellow axis).
  Even if your movie width and height are not multiples of 16, the
  encoder will use enough 16x16 macroblocks to cover the whole picture
  area, and the extra space will go to waste.
  So in the interests of maximizing quality at a fixed filesize, it is
  a bad idea to use dimensions that are not multiples of 16.
</para>

<para>
  Most DVDs also have some degree of black borders at the edges. Leaving
  these in place can hurt quality in several ways.
</para>

<orderedlist>
<listitem>
<para>
  MPEG-type compression is also highly dependent on frequency domain
  transformations, in particular the Discrete Cosine Transform (DCT),
  which is similar to the Fourier transform. This sort of encoding is
  efficient for representing patterns and smooth transitions, but it
  has a hard time with sharp edges. In order to encode them it must
  use many more bits, or else an artifact known as ringing will
  appear.
</para>

<para>
  The frequency transform (DCT) takes place separately on each
  macroblock (actually each block), so this problem only applies when
  the sharp edge is inside a block. If your black borders begin
  exactly at multiple-of-16 pixel boundaries, this is not a problem.
  However, the black borders on DVDs rarely come nicely aligned, so
  in practice you will always need to crop to avoid this penalty.
</para>
</listitem>
</orderedlist>

<para>
  In addition to frequency domain transforms, MPEG-type compression uses
  motion vectors to represent the change from one frame to the next.
  Motion vectors naturally work much less efficiently for new content
  coming in from the edges of the picture, because it is not present in
  the previous frame. As long as the picture extends all the way to the
  edge of the encoded region, motion vectors have no problem with
  content moving out the edges of the picture. However, in the presence
  of black borders, there can be trouble:
</para>

<orderedlist continuation="continues">
<listitem>
<para>
  For each macroblock, MPEG-type compression stores a vector
  identifying which part of the previous frame should be copied into
  this macroblock as a base for predicting the next frame. Only the
  remaining differences need to be encoded. If a macroblock spans the
  edge of the picture and contains part of the black border, then
  motion vectors from other parts of the picture will overwrite the
  black border. This means that lots of bits must be spent either
  re-blackening the border that was overwritten, or (more likely) a
  motion vector will not be used at all and all the changes in this
  macroblock will have to be coded explicitly. Either way, encoding
  efficiency is greatly reduced.
</para>

<para>
  Again, this problem only applies if black borders do not line up on
  multiple-of-16 boundaries.
</para>
</listitem>

<listitem>
<para>
  Finally, suppose we have a macroblock in the interior of the
  picture, and an object is moving into this block from near the edge
  of the image. MPEG-type coding cannot say "copy the part that is
  inside the picture but not the black border." So the black border
  will get copied inside too, and lots of bits will have to be spent
  encoding the part of the picture that is supposed to be there.
</para>

<para>
  If the picture runs all the way to the edge of the encoded area,
  MPEG has special optimizations to repeatedly copy the pixels at the
  edge of the picture when a motion vector comes from outside the
  encoded area. This feature becomes useless when the movie has black
  borders. Unlike problems 1 and 2, aligning the borders at multiples
  of 16 does not help here.
</para>
</listitem>

<listitem>
<para>
  Despite the borders being entirely black and never changing, there
  is at least a minimal amount of overhead involved in having more
  macroblocks.
</para>
</listitem>
</orderedlist>

<para>
  For all of these reasons, it is recommended to fully crop black
  borders. Further, if there is an area of noise/distortion at the edge
  of the picture, cropping this will improve encoding efficiency as
  well. Videophile purists who want to preserve the original as close as
  possible may object to this cropping, but unless you plan to encode at
  constant quantizer, the quality you gain from cropping will
  considerably exceed the amount of information lost at the edges.
</para>
</sect2>


<sect2 id="menc-feat-dvd-mpeg4-crop">
<title>Cropping and Scaling</title>

<para>
  Recall from the previous section that the final picture size you
  encode should be a multiple of 16 (in both width and height).
  This can be achieved by cropping, scaling, or a combination of both.
</para>

<para>
  When cropping, there are a few guidelines that must be followed to
  avoid damaging your movie.
  The normal YUV format, 4:2:0, stores chroma (color) information
  subsampled, i.e. chroma is only sampled half as often in each
  direction as luma (intensity) information.
  Observe this diagram, where L indicates luma sampling points and C
  chroma.
</para>

<informaltable>
<?dbhtml table-width="40%" ?>
<?dbfo table-width="40%" ?>
<tgroup cols="8" align="center">
<colspec colnum="1" colname="col1"/>
<colspec colnum="2" colname="col2"/>
<colspec colnum="3" colname="col3"/>
<colspec colnum="4" colname="col4"/>
<colspec colnum="5" colname="col5"/>
<colspec colnum="6" colname="col6"/>
<colspec colnum="7" colname="col7"/>
<colspec colnum="8" colname="col8"/>
<spanspec spanname="spa1-2" namest="col1" nameend="col2"/>
<spanspec spanname="spa3-4" namest="col3" nameend="col4"/>
<spanspec spanname="spa5-6" namest="col5" nameend="col6"/>
<spanspec spanname="spa7-8" namest="col7" nameend="col8"/>
  <tbody>
    <row>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
    </row>
    <row>
      <entry spanname="spa1-2">C</entry>
      <entry spanname="spa3-4">C</entry>
      <entry spanname="spa5-6">C</entry>
      <entry spanname="spa7-8">C</entry>
    </row>
    <row>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
    </row>
    <row>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
    </row>
    <row>
      <entry spanname="spa1-2">C</entry>
      <entry spanname="spa3-4">C</entry>
      <entry spanname="spa5-6">C</entry>
      <entry spanname="spa7-8">C</entry>
    </row>
    <row>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
    </row>
  </tbody>
</tgroup>
</informaltable>

<para>
  As you can see, rows and columns of the image naturally come in pairs.
  Thus your crop offsets and dimensions <emphasis>must</emphasis> be
  even numbers.
  If they are not, the chroma will no longer line up correctly with the
  luma.
  In theory, it is possible to crop with odd offsets, but it requires
  resampling the chroma which is potentially a lossy operation and not
  supported by the crop filter.
</para>

<para>
  Further, interlaced video is sampled as follows:
</para>

<informaltable>
<?dbhtml table-width="80%" ?>
<?dbfo table-width="80%" ?>
<tgroup cols="16" align="center">
<colspec colnum="1"  colname="col1"/>
<colspec colnum="2"  colname="col2"/>
<colspec colnum="3"  colname="col3"/>
<colspec colnum="4"  colname="col4"/>
<colspec colnum="5"  colname="col5"/>
<colspec colnum="6"  colname="col6"/>
<colspec colnum="7"  colname="col7"/>
<colspec colnum="8"  colname="col8"/>
<colspec colnum="9"  colname="col9"/>
<colspec colnum="10" colname="col10"/>
<colspec colnum="11" colname="col11"/>
<colspec colnum="12" colname="col12"/>
<colspec colnum="13" colname="col13"/>
<colspec colnum="14" colname="col14"/>
<colspec colnum="15" colname="col15"/>
<colspec colnum="16" colname="col16"/>
<spanspec spanname="spa1-2"   namest="col1" nameend="col2"/>
<spanspec spanname="spa3-4"   namest="col3" nameend="col4"/>
<spanspec spanname="spa5-6"   namest="col5" nameend="col6"/>
<spanspec spanname="spa7-8"   namest="col7" nameend="col8"/>
<spanspec spanname="spa9-10"  namest="col9" nameend="col10"/>
<spanspec spanname="spa11-12" namest="col11" nameend="col12"/>
<spanspec spanname="spa13-14" namest="col13" nameend="col14"/>
<spanspec spanname="spa15-16" namest="col15" nameend="col16"/>
  <tbody>
    <row>
      <entry namest="col1" nameend="col8">Top field</entry>
      <entry namest="col9" nameend="col16">Bottom field</entry>
    </row>
    <row>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
    </row>
    <row>
      <entry spanname="spa1-2">C</entry>
      <entry spanname="spa3-4">C</entry>
      <entry spanname="spa5-6">C</entry>
      <entry spanname="spa7-8">C</entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
    </row>
    <row>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
    </row>
    <row>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
    </row>
    <row>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry spanname="spa9-10">C</entry>
      <entry spanname="spa11-12">C</entry>
      <entry spanname="spa13-14">C</entry>
      <entry spanname="spa15-16">C</entry>
    </row>
    <row>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
    </row>
    <row>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
    </row>
    <row>
      <entry spanname="spa1-2">C</entry>
      <entry spanname="spa3-4">C</entry>
      <entry spanname="spa5-6">C</entry>
      <entry spanname="spa7-8">C</entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
    </row>
    <row>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
    </row>
    <row>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
    </row>
    <row>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry spanname="spa9-10">C</entry>
      <entry spanname="spa11-12">C</entry>
      <entry spanname="spa13-14">C</entry>
      <entry spanname="spa15-16">C</entry>
    </row>
    <row>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
      <entry>L</entry>
    </row>
  </tbody>
</tgroup>
</informaltable>

<para>
  As you can see, the pattern does not repeat until after 4 lines.
  So for interlaced video, your y-offset and height for cropping must
  be multiples of 4.
</para>

<para>
  Native DVD resolution is 720x480 for NTSC, and 720x576 for PAL, but
  there is an aspect flag that specifies whether it is full-screen (4:3) or
  wide-screen (16:9). Many (if not most) widescreen DVDs are not strictly
  16:9, and will be either 1.85:1 or 2.35:1 (cinescope). This means that
  there will be black bands in the video that will need to be cropped out.
</para>

<para>
  <application>MPlayer</application> provides a crop detection filter that
  will determine the crop rectangle (<option>-vf cropdetect</option>).
  Run <application>MPlayer</application> with
  <option>-vf cropdetect</option> and it will print out the crop
  settings to remove the borders.
  You should let the movie run long enough that the whole picture
  area is used, in order to get accurate crop values.
</para>

<para>
  Then, test the values you get with <application>MPlayer</application>,
  using the command line which was printed by
  <option>cropdetect</option>, and adjust the rectangle as needed.
  The <option>rectangle</option> filter can help by allowing you to
  interactively position the crop rectangle over your movie.
  Remember to follow the above divisibility guidelines so that you
  do not misalign the chroma planes.
</para>

<para>
  In certain cases, scaling may be undesirable.
  Scaling in the vertical direction is difficult with interlaced
  video, and if you wish to preserve the interlacing, you should
  usually refrain from scaling.
  If you will not be scaling but you still want to use multiple-of-16
  dimensions, you will have to overcrop.
  Do not undercrop, since black borders are very bad for encoding!
</para>

<para>
  Because MPEG-4 uses 16x16 macroblocks, you will want to make sure that each
  dimension of the video you are encoding is a multiple of 16 or else you
  will be degrading quality, especially at lower bitrates. You can do this
  by rounding the width and height of the crop rectangle down to the nearest
  multiple of 16.
  As stated earlier, when cropping, you will want to increase the Y offset by
  half the difference of the old and the new height so that the resulting
  video is taken from the center of the frame. And because of the way DVD
  video is sampled, make sure the offset is an even number. (In fact, as a
  rule, never use odd values for any parameter when you are cropping and
  scaling video.) If you are not comfortable throwing a few extra pixels
  away, you might prefer instead to scale the video instead. We will look
  at this in our example below.
  You can actually let the <option>cropdetect</option> filter do all of the
  above for you, as it has an optional <option>round</option> parameter that
  is equal to 16 by default.
</para>

<para>
  Also, be careful about "half black" pixels at the edges. Make sure you
  crop these out too, or else you will be wasting bits there that
  are better spent elsewhere.
</para>

<para>
  After all is said and done, you will probably end up with video whose pixels
  are not quite 1.85:1 or 2.35:1, but rather something close to that. You
  could calculate the new aspect ratio manually, but
  <application>MEncoder</application> offers an option for <systemitem
  class="library">libavcodec</systemitem> called <option>autoaspect</option>
  that will do this for you. Absolutely do not scale this video up in order to
  square the pixels unless you like to waste your hard disk space. Scaling
  should be done on playback, and the player will use the aspect stored in
  the AVI to determine the correct resolution.
  Unfortunately, not all players enforce this auto-scaling information,
  therefore you may still want to rescale.
</para>
</sect2>


<sect2 id="menc-feat-dvd-mpeg4-resolution-bitrate">
<title>Choosing resolution and bitrate</title>

<para>
  If you will not be encoding in constant quantizer mode, you need to
  select a bitrate.
  The concept of bitrate is quite simple.
  It is the (average) number of bits that will be consumed to store your
  movie, per second.
  Normally bitrate is measured in kilobits (1000 bits) per second.
  The size of your movie on disk is the bitrate times the length of the
  movie in time, plus a small amount of "overhead" (see the section on
  <link linkend="menc-feat-dvd-mpeg4-muxing-avi-limitations">the AVI container</link>
  for instance).
  Other parameters such as scaling, cropping, etc. will
  <emphasis role="bold">not</emphasis> alter the file size unless you
  change the bitrate as well!.
</para>
<para>
  Bitrate does <emphasis role="bold">not</emphasis> scale proportionally
  to resolution.
  That is to say, a 320x240 file at 200 kbit/sec will not be the same
  quality as the same movie at 640x480 and 800 kbit/sec!
  There are two reasons for this:
<orderedlist>
  <listitem><para>
    <emphasis role="bold">Perceptual</emphasis>: You notice MPEG
    artifacts more if they are scaled up bigger!
    Artifacts appear on the scale of blocks (8x8).
    Your eye will not see errors in 4800 small blocks as easily as it
    sees errors in 1200 large blocks (assuming you will be scaling both
    to fullscreen).
  </para></listitem>
  <listitem><para>
    <emphasis role="bold">Theoretical</emphasis>: When you scale down
    an image but still use the same size (8x8) blocks for the frequency
    space transform, you move more data to the high frequency bands.
    Roughly speaking, each pixel contains more of the detail than it
    did before.
    So even though your scaled-down picture contains 1/4 the information
    in the spacial directions, it could still contain a large portion
    of the information in the frequency domain (assuming that the high
    frequencies were underutilized in the original 640x480 image).
  </para></listitem>
  </orderedlist>
</para>
<para>
  Past guides have recommended choosing a bitrate and resolution based
  on a "bits per pixel" approach, but this is usually not valid due to
  the above reasons.
  A better estimate seems to be that bitrates scale proportional to the
  square root of resolution, so that 320x240 and 400 kbit/sec would be
  comparable to 640x480 at 800 kbit/sec.
  However this has not been verified with theoretical or empirical
  rigor.
  Further, given that movies vary greatly with regard to noise, detail,
  degree of motion, etc., it is futile to make general recommendations
  for bits per length-of-diagonal (the analog of bits per pixel,
  using the square root).
</para>
<para>
  So far we have discussed the difficulty of choosing a bitrate and
  resolution.
</para>


<sect3 id="menc-feat-dvd-mpeg4-resolution-bitrate-compute">
<title>Computing the resolution</title>
<para>
  First, you should compute the encoded aspect ratio:
  <systemitem>ARc = (Wc x (ARa / PRdvd )) / Hc</systemitem>
<itemizedlist>
<title>where:</title>
<listitem><para>
  Wc and Hc are the width and height of the cropped video,
</para></listitem>
<listitem><para>
  ARa is the displayed aspect ratio, which usually is 4/3 or 16/9,
</para></listitem>
<listitem><para>
  PRdvd is the pixel ratio of the DVD which is equal to 1.25=(720/576) for PAL
  DVDs and 1.5=(720/480) for NTSC DVDs,
</para></listitem>
</itemizedlist>
</para>

<para>
  Then, you can compute the X and Y resolution, according to a certain
  Compression Quality (CQ) factor:
  <systemitem>ResY = INT(SQRT( 1000*Bitrate/25/ARc/CQ )/16) * 16</systemitem>
  and
  <systemitem>ResX = INT( ResY * ARc / 16) * 16</systemitem>
</para>

<para>
  Okay, but what is the CQ?
  The CQ represents the number of bits per pixel and per frame of the encode.
  Roughly speaking, the greater the CQ, the less the likelihood to see
  encoding artifacts.
  However, if you have a target size for your movie (1 or 2 CDs for instance),
  there is a limited total number of bits that you can spend; therefore it is
  necessary to find a good tradeoff between compressibility and quality.
</para>

<para>
  The CQ depends both on the bitrate and the movie resolution.
  In order to raise the CQ, typically you would downscale the movie given that the
  bitrate is computed in function of the target size and the length of the
  movie, which are constant.
  A CQ below 0.18 usually ends up in a very blocky picture, because there
  are not enough bits to code the information of each macroblock (MPEG4, like
  many other codecs, groups pixels by blocks of several pixels to compress the
  image; if there are not enough bits, the edges of those blocks are
  visible).
  It is therefore wise to take a CQ ranging from 0.20 to 0.22 for a 1 CD rip,
  and 0.26-0.28 for 2 CDs.
</para>

<para>
  Please take note that the CQ is just an indicative figure, as depending on
  the encoded content, a CQ of 0.18 may look just fine for a Bergman, contrary
  to a movie such as The Matrix, which contains many high-motion scenes.
  On the other hand, it is worthless to raise CQ higher than 0.30 as you would
  be wasting bits without any noticeable quality gain.
</para>
</sect3>

</sect2>

<sect2 id="menc-feat-dvd-mpeg4-filtering">
<title>Filtering</title>

<para>
  Learning how to use <application>MEncoder</application>'s video filters
  is essential to producing good encodes.
  All video processing is performed through the filters -- cropping,
  scaling, color adjustment, noise removal, sharpening, deinterlacing,
  telecine, inverse telecine, and deblocking, just to name a few.
  Along with the vast number of supported input formats, the variety of
  filters available in <application>MEncoder</application> is one of its
  main advantages over other similar programs.
</para>

<para>
  Filters are loaded in a chain using the -vf option:

  <screen>-vf filter1=options,filter2=options,...</screen>

  Most filters take several numeric options separated by colons, but
  the syntax for options varies from filter to filter, so read the man
  page for details on the filters you wish to use.
</para>

<para>
  Filters operate on the video in the order they are loaded.
  For example, the following chain:

  <screen>-vf crop=688:464:12:4,scale=640:464</screen>

  will first crop the 688x464 region of the picture with upper-left
  corner at (12,4), and then scale the result down to 640x464.
</para>

<para>
  Certain filters need to be loaded at or near the beginning of the
  filter chain, in order to take advantage of information from the
  video decoder that will be lost or invalidated by other filters.
  The principal examples are <option>pp</option> (postprocessing, only
  when it is performing deblock or dering operations),
  <option>spp</option> (another postprocessor to remove MPEG artifacts),
  <option>pullup</option> (inverse telecine), and
  <option>softpulldown</option> (for converting soft telecine to hard
  telecine).
</para>

<para>
  In general, you want to do as little filtering as possible to the movie
  in order to remain close to the original DVD source. Cropping is often
  necessary (as described above), but avoid to scale the video. Although
  scaling down is sometimes preferred to using higher quantizers, we want
  to avoid both these things: remember that we decided from the start to
  trade bits for quality.
</para>

<para>
  Also, do not adjust gamma, contrast, brightness, etc. What looks good
  on your display may not look good on others. These adjustments should
  be done on playback only.
</para>

<para>
  One thing you might want to do, however, is pass the video through a
  very light denoise filter, such as <option>-vf hqdn3d=2:1:2</option>.
  Again, it is a matter of putting those bits to better use: why waste them
  encoding noise when you can just add that noise back in during playback?
  Increasing the parameters for <option>hqdn3d</option> will further
  improve compressibility, but if you increase the values too much, you
  risk degrading the image visibily. The suggested values above
  (<option>2:1:2</option>) are quite conservative; you should feel free to
  experiment with higher values and observe the results for yourself.
</para>

</sect2>


<sect2 id="menc-feat-dvd-mpeg4-interlacing">
<title>Interlacing and Telecine</title>

<para>
  Almost all movies are shot at 24 fps. Because NTSC is 30000/1001 fps, some
  processing must be done to this 24 fps video to make it run at the correct
  NTSC framerate. The process is called 3:2 pulldown, commonly referred to
  as telecine (because pulldown is often applied during the telecine
  process), and, naively described, it works by slowing the film down to
  24000/1001 fps, and repeating every fourth frame.
</para>

<para>
  No special processing, however, is done to the video for PAL DVDs, which
  run at 25 fps. (Technically, PAL can be telecined, called 2:2 pulldown,
  but this does not become an issue in practice.) The 24 fps film is simply
  played back at 25 fps. The result is that the movie runs slightly faster,
  but unless you are an alien, you probably will not notice the difference.
  Most PAL DVDs have pitch-corrected audio, so when they are played back at
  25 fps things will sound right, even though the audio track (and hence the
  whole movie) has a running time that is 4% less than NTSC DVDs.
</para>

<para>
  Because the video in a PAL DVD has not been altered, you need not worry
  much about framerate. The source is 25 fps, and your rip will be 25
  fps. However, if you are ripping an NTSC DVD movie, you may need to
  apply inverse telecine.
</para>

<para>
  For movies shot at 24 fps, the video on the NTSC DVD is either telecined
  30000/1001, or else it is progressive 24000/1001 fps and intended to be telecined
  on-the-fly by a DVD player. On the other hand, TV series are usually
  only interlaced, not telecined. This is not a hard rule: some TV series
  are interlaced (such as Buffy the Vampire Slayer) whereas some are a
  mixture of progressive and interlaced (such as Angel, or 24).
</para>

<para>
  It is highly recommended that you read the section on
  <link linkend="menc-feat-telecine">How to deal with telecine and interlacing in NTSC DVDs</link>
  to learn how to handle the different possibilities.
</para>

<para>
  However, if you are mostly just ripping movies, likely you are either
  dealing with 24 fps progressive or telecined video, in which case you can
  use the <option>pullup</option> filter <option>-vf
  pullup,softskip</option>.
</para>

</sect2>

<sect2 id="menc-feat-dvd-mpeg4-encoding-interlaced">
<title>Encoding interlaced video</title>

<para>
  If the movie you want to encode is interlaced (NTSC video or
  PAL video), you will need to choose whether you want to
  deinterlace or not.
  While deinterlacing will make your movie usable on progressive
  scan displays such a computer monitors and projectors, it comes
  at a cost: The fieldrate of 50 or 60000/1001 fields per second
  is halved to 25 or 30000/1001 frames per second, and roughly half of
  the information in your movie will be lost during scenes with
  significant motion.
</para>

<para>
  Therefore, if you are encoding for high quality archival purposes,
  it is recommended not to deinterlace.
  You can always deinterlace the movie at playback time when
  displaying it on progressive scan devices, and future players will
  be able to deinterlace to full fieldrate, interpolating 50 or
  60000/1001 entire frames per second from the interlaced video.
</para>

<para>
Special care must be taken when working with interlaced video:
</para>

<orderedlist>
<listitem><para>
  Crop height and y-offset must be multiples of 4.
</para></listitem>
<listitem><para>
  Any vertical scaling must be performed in interlaced mode.
</para></listitem>
<listitem><para>
  Postprocessing and denoising filters may not work as expected
  unless you take special care to operate them a field at a time,
  and they may damage the video if used incorrectly.
</para></listitem>
</orderedlist>

<para>
With these things in mind, here is our first example:
</para>
<screen>
  mencoder <replaceable>capture.avi</replaceable> -mc 0 -oac lavc -ovc lavc -lavcopts \
  vcodec=mpeg2video:vbitrate=6000:ilme:ildct:acodec=mp2:abitrate=224
</screen>
<para>
Note the <option>ilme</option> and <option>ildct</option> options. 
</para>
</sect2>


<sect2 id="menc-feat-dvd-mpeg4-av-sync">
<title>Notes on Audio/Video synchronization</title>
<para>
<application>MEncoder</application>'s audio/video synchronization
algorithms were designed with the intention of recovering files with
broken sync.
However, in some cases they can cause unnecessary skipping and duplication of
frames, and possibly slight A/V desync, when used with proper input
(of course, A/V sync issues apply only if you process or copy the
audio track while transcoding the video, which is strongly encouraged).
Therefore, you may have to switch to basic A/V sync with
the <option>-mc 0</option> option, or put this in your
<systemitem>~/.mplayer/mencoder</systemitem> config file, as long as
you are only working with good sources (DVD, TV capture, high quality
MPEG-4 rips, etc) and not broken ASF/RM/MOV files.
</para>
<para>
If you want to further guard against strange frame skips and
duplication, you can use both <option>-mc 0</option> and
<option>-noskip</option>.
This will prevent <emphasis>all</emphasis> A/V sync, and copy frames
one-to-one, so you cannot use it if you will be using any filters that
unpredictably add or drop frames, or if your input file has variable
framerate!
Therefore, using <option>-noskip</option> is not in general recommended.
</para>
<para>
The so-called "three-pass" audio encoding which <application>MEncoder</application>
supports has been reported to cause A/V desync.
This will definitely happen if it is used in conjunction with certain
filters, therefore, it is now recommended <emphasis>not</emphasis> to
use three-pass audio mode.
This feature is only left for compatibility purposes and for expert
users who understand when it is safe to use and when it is not.
If you have never heard of three-pass mode before, forget that we
even mentioned it!
</para>
<para>
There have also been reports of A/V desync when encoding from stdin
with <application>MEncoder</application>.
Do not do this! Always use a file or CD/DVD/etc device as input.
</para>
</sect2>

<sect2 id="menc-feat-dvd-mpeg4-audio">
<title>Audio</title>

<para>
  Audio is a much simpler problem to solve: if you care about quality, just
  leave it as is.
  Even AC3 5.1 streams are at most 448Kbit/s, and they are worth every bit.
  You might be tempted to transcode the audio to high quality Vorbis, but
  just because you do not have an A/V receiver for AC3 pass-through today
  does not mean you will not have one tomorrow. Future-proof your DVD rips by
  preserving the AC3 stream.
  You can keep the AC3 stream either by copying it directly into the video
  stream <link linkend="menc-feat-mpeg4">during the encoding</link>.
  You can also extract the AC3 stream in order to mux it into containers such
  as NUT or Matroska.
  <screen>mplayer <replaceable>source_file.vob</replaceable> -aid 129 -dumpaudio -dumpfile <replaceable>sound.ac3</replaceable></screen>
  will dump into the file <replaceable>sound.ac3</replaceable> the
  audio track number 129 from the file
  <replaceable>source_file.vob</replaceable> (NB: DVD VOB files
  usually use a different audio numbering,
  which means that the VOB audio track 129 is the 2nd audio track of the file).
</para>

<para>
  But sometimes you truly have no choice but to further compress the
  sound so that more bits can be spent on the video.
  Most people choose to compress audio with either MP3 or Vorbis audio
  codecs.
  While the latter is a very space-efficient codec, MP3 is better supported
  by hardware players, although this trend is changing.
</para>

<para>
  Do <emphasis>not</emphasis> use <option>-nosound</option> when encoding
  a file with audio, even if you will be encoding and muxing audio
  separately later.
  Though it may work in ideal cases, using <option>-nosound</option> is
  likely to hide some problems in your encoding command line setting.
  In other words, having a soundtrack during your encode assures you that,
  provided you do not see messages such as
  <quote>Too many audio packets in the buffer</quote>, you will be able
  to get proper sync.
</para>

<para>
  You need to have <application>MEncoder</application> process the sound.
  You can for example copy the orignal soundtrack during the encode with
  <option>-oac copy</option> or convert it to a "light" 4 kHz mono WAV
  PCM with <option>-oac pcm -channels 1 -srate 4000</option>.
  Otherwise, in some cases, it will generate a video file that will not sync
  with the audio.
  Such cases are when the number of video frames in the source file does
  not match up to the total length of audio frames or whenever there
  are discontinuities/splices where there are missing or extra audio frames.
  The correct way to handle this kind of problem is to insert silence or
  cut audio at these points.
  However <application>MPlayer</application> cannot do that, so if you
  demux the AC3 audio and encode it with a separate app (or dump it to PCM with
  <application>MPlayer</application>), the splices will be left incorrect
  and the only way to correct them is to drop/dup video frames at the
  splice.
  As long as <application>MEncoder</application> sees the audio when it is
  encoding the video, it can do this dropping/duping (which is usually OK
  since it takes place at full black/scenechange, but if
  <application>MEncoder</application> cannot see the audio, it will just
  process all frames as-is and they will not fit the final audio stream when
  you for example merge your audio and video track into a Matroska file.
</para>

<para>
  First of all, you will have to convert the DVD sound into a WAV file that the
  audio codec can use as input.
  For example:
  <screen>mplayer <replaceable>source_file.vob</replaceable> -ao pcm:file=<replaceable>destination_sound.wav</replaceable> -vc dummy -aid 1 -vo null</screen>
  will dump the second audio track from the file
  <replaceable>source_file.vob</replaceable> into the file
  <replaceable>destination_sound.wav</replaceable>.
  You may want to normalize the sound before encoding, as DVD audio tracks
  are commonly recorded at low volumes.
  You can use the tool <application>normalize</application> for instance,
  which is available in most distributions.
  If you are using Windows, a tool such as <application>BeSweet</application>
  can do the same job.
  You will compress in either Vorbis or MP3.
  For example:
  <screen>oggenc -q1 <replaceable>destination_sound.wav</replaceable></screen>
  will encode <replaceable>destination_sound.wav</replaceable> with
  the encoding quality 1, which is roughly equivalent to 80Kb/s, and
  is the minimum quality at which you should encode if you care about
  quality.
  Please note that MEncoder currently cannot mux Vorbis audio tracks
  into the output file because it only supports AVI and MPEG
  containers as an output, each of which may lead to audio/video
  playback synchronization problems with some players when the AVI file
  contain VBR audio streams such as Vorbis.
  Do not worry, this document will show you how you can do that with third
  party programs.
</para>

</sect2>


<sect2 id="menc-feat-dvd-mpeg4-muxing">
<title>Muxing</title>
<para>
  Now that you have encoded your video, you will most likely want
  to mux it with one or more audio tracks into a movie container, such
  as AVI, MPEG, Matroska or NUT.
  <application>MEncoder</application> is currently only able to natively output
  audio and video into MPEG and AVI container formats.
  for example:
  <screen>mencoder -oac copy -ovc copy  -o <replaceable>output_movie.avi</replaceable> -audiofile <replaceable>input_audio.mp2</replaceable> <replaceable>input_video.avi</replaceable></screen>
  This would merge the video file <replaceable>input_video.avi</replaceable>
  and the audio file <replaceable>input_audio.mp2</replaceable>
  into the AVI file <replaceable>output_movie.avi</replaceable>.
  This command works with MPEG-1 layer I, II and III (more commonly known
  as MP3) audio, WAV and a few other audio formats too.
</para>

<para>
  MEncoder features experimental support for
  <systemitem class="library">libavformat</systemitem>, which is a
  library from the FFmpeg project that supports muxing and demuxing
  a variety of containers.
  For example:
  <screen>mencoder -oac copy -ovc copy  -o <replaceable>output_movie.asf</replaceable> -audiofile <replaceable>input_audio.mp2</replaceable> <replaceable>input_video.avi</replaceable> -of lavf -lavfopts format=asf</screen>
  This will do the same thing as the previous example, except that
  the output container will be ASF.
  Please note that this support is highly experimental (but getting
  better every day), and will only work if you compiled
  <application>MPlayer</application> with the support for
  <systemitem class="library">libavformat</systemitem> enabled (which
  means that a pre-packaged binary version will not work in most cases).
</para>


<sect3 id="menc-feat-dvd-mpeg4-muxing-filter-issues">
<title>Improving muxing and A/V sync reliability</title>
<para>
  You may experience some serious A/V sync problems while trying to mux
  your video and some audio tracks, where no matter how you adjust the
  audio delay, you will never get proper sync.
  That may happen when you use some video filters that will drop or
  duplicate some frames, like the inverse telecine filters.
  It is strongly encouraged to append the <option>harddup</option> video
  filter at the end of the filter chain to avoid this kind of problem.
</para>

<para>
  Without <option>harddup</option>, if <application>MEncoder</application>
  wants to duplicate a frame, it relies on the muxer to put a mark on the
  container so that the last frame will be displayed again to maintain
  sync while writing no actual frame.
  With <option>harddup</option>, <application>MEncoder</application>
  will instead just push the last frame displayed again into the filter
  chain.
  This means that the encoder receives the <emphasis>exact</emphasis>
  same frame twice, and compresses it.
  This will result in a slightly bigger file, but will not cause problems
  when demuxing or remuxing into other container formats.
</para>

<para>
  You may also have no choice but to use <option>harddup</option> with
  container formats that are not too tightly linked with
  <application>MEncoder</application> such as the ones supported through
  <systemitem class="library">libavformat</systemitem>, which may not
  support frame duplication at the container level.
</para>
</sect3>


<sect3 id="menc-feat-dvd-mpeg4-muxing-avi-limitations">
<title>Limitations of the AVI container</title>
<para>
  Although it is the most widely-supported container format after MPEG-1,
  AVI also has some major drawbacks.
  Perhaps the most obvious is the overhead.
  For each chunk of the AVI file, 24 bytes are wasted on headers and
  index.
  This translates into a little over 5 MB per hour, or 1-2.5%
  overhead for a 700 MB movie. This may not seem like much, but it could
  mean the difference between being able to use 700 kbit/sec video or
  714 kbit/sec, and every bit of quality counts.
</para>

<para>
  In addition this gross inefficiency, AVI also has the following major
  limitations:
</para>

<orderedlist>
<listitem>
<para>
  Only fixed-fps content can be stored. This is particularly limiting
  if the original material you want to encode is mixed content, for
  example a mix of NTSC video and film material.
  Actually there are hacks that can be used to store mixed-framerate
  content in AVI, but they increase the (already huge) overhead
  fivefold or more and so are not practical.
</para>
</listitem>
<listitem>
<para>
  Audio in AVI files must be either constant-bitrate (CBR) or
  constant-framesize (i.e. all frames decode to the same number of
  samples).
  Unfortunately, the most efficient codec, Vorbis, does not meet
  either of these requirements.
  Therefore, if you plan to store your movie in AVI, you will have to
  use a less efficient codec such as MP3 or AC3.
</para>
</listitem>
</orderedlist>

<para>
  Having said all that, <application>MEncoder</application> does not
  currently support variable-fps output or Vorbis encoding.
  Therefore, you may not see these as limitations if
  <application>MEncoder</application> is the
  only tool you will be using to produce your encodes.
  However, it is possible to use <application>MEncoder</application>
  only for video encoding, and then use external tools to encode
  audio and mux it into another container format.
</para>
</sect3>

<sect3 id="menc-feat-dvd-mpeg4-muxing-matroska">
<title>Muxing into the Matroska container</title>
<para>
  Matroska is a free, open standard container format, aiming
  to offer a lot of advanced features, which older containers
  like AVI cannot handle.
  For example, Matroska supports variable bitrate audio content
  (VBR), variable framerates (VFR), chapters, file attachments,
  error detection code (EDC) and modern A/V Codecs like "Advanced Audio
  Coding" (AAC), "Vorbis" or "MPEG-4 AVC" (H.264), next to nothing
  handled by AVI.
</para>

<para>
  The tools required to create Matroska files are collectively called
  <application>mkvtoolnix</application>, and are available for most
  Unix platforms as well as <application>Windows</application>.
  Because Matroska is an open standard you may find other
  tools that suit you better, but since mkvtoolnix is the most
  common, and is supported by the Matroska team itself, we will
  only cover its usage.
</para>

<para>
  Probably the easiest way to get started with Matroska is to use 
  <application>MMG</application>, the graphical frontend shipped with
  <application>mkvtoolnix</application>, and follow the
  <ulink url="http://www.bunkus.org/videotools/mkvtoolnix/doc/mkvmerge-gui.html">guide to mkvmerge GUI (mmg)</ulink>
</para>

<para>
  You may also mux audio and video files using the command line:
  <screen>mkvmerge -o <replaceable>output.mkv</replaceable> <replaceable>input_video.avi</replaceable> <replaceable>input_audio1.mp3</replaceable> <replaceable>input_audio2.ac3</replaceable></screen>
  This would merge the video file <replaceable>input_video.avi</replaceable>
  and the two audio files <replaceable>input_audio1.mp3</replaceable>
  and <replaceable>input_audio2.ac3</replaceable> into the Matroska
  file <replaceable>output.mkv</replaceable>.
  Matroska, as mentioned earlier, is able to do much more than that, like
  multiple audio tracks (including fine-tuning of audio/video
  synchronization), chapters, subtitles, splitting, etc...
  Please refer to the documentation of those applications for
  more details.
</para>

</sect3>

</sect2>

</sect1>

<sect1 id="menc-feat-telecine">
<title>How to deal with telecine and interlacing within NTSC DVDs</title>

<sect2 id="menc-feat-telecine-intro">
<title>Introduction</title>
<formalpara>
<title>What is telecine?</title>
<para>
  I suggest you visit this page if you do not understand much of what
  is written in this document:
  <ulink url="http://www.divx.com/support/guides/guide.php?gid=10">http://www.divx.com/support/guides/guide.php?gid=10</ulink>
  This URL links to an understandable and reasonably comprehensive
  description of what telecine is.
</para></formalpara>

<formalpara>
<title>A note about the numbers.</title>
<para>
  Many documents, including the guide linked above, refer to the fields
  per second value of NTSC video as 59.94 and the corresponding frames
  per second values as 29.97 (for telecined and interlaced) and 23.976
  (for progressive). For simplicity, some documents even round these
  numbers to 60, 30, and 24.
</para></formalpara>

<para>
  Strictly speaking, all those numbers are approximations. Black and
  white NTSC video was exactly 60 fields per second, but 60000/1001
  was later chosen to accomodate color data while remaining compatible
  with contemporary black and white televisions. Digital NTSC video
  (such as on a DVD) is also 60000/1001 fields per second. From this,
  interlaced and telecined video are derived to be 30000/1001 frames
  per second; progressive video is 24000/1001 frames per second.
</para>

<para>
  Older versions of the <application>MEncoder</application> documentation
  and many archived mailing list posts refer to 59.94, 29.97, and 23.976.
  All <application>MEncoder</application> documentation has been updated
  to use the fractional values, and you should use them too.
</para>

<para>
  <option>-ofps 23.976</option> is incorrect.
  <option>-ofps 24000/1001</option> should be used instead.
</para>

<formalpara>
<title>How telecine is used.</title>
<para>
  All video intended to be displayed on an NTSC
  television set must be 60000/1001 fields per second. Made-for-TV movies
4  and shows are often filmed directly at 60000/1001 fields per second, but
  the majority of cinema is filmed at 24 or 24000/1001 frames per
  second. When cinematic movie DVDs are mastered, the video is then
  converted for television using a process called telecine.
</para></formalpara>

<para>
  On a DVD, the video is never actually stored as 60000/1001 fields per
  second. For video that was originally 60000/1001, each pair of fields is
  combined to form a frame, resulting in 30000/1001 frames per
  second. Hardware DVD players then read a flag embedded in the video
  stream to determine whether the odd- or even-numbered lines should
  form the first field.
</para>

<para>
  Usually, 24000/1001 frames per second content stays as it is when
  encoded for a DVD, and the DVD player must perform telecining
  on-the-fly. Sometimes, however, the video is telecined
  <emphasis>before</emphasis> being stored on the DVD; even though it
  was originally 24000/1001 frames per second, it becomes 60000/1001 fields per
  second. When it is stored on the DVD, pairs of fields are combined to form
  30000/1001 frames per second.
</para>

<para>
  When looking at individual frames formed from 60000/10001 fields per
  second video, telecined or otherwise, interlacing is clearly visible
  wherever there is any motion, because one field (say, the
  even-numbered lines) represents a moment in time 1/(60000/1001)
  seconds later than the other. Playing interlaced video on a computer
  looks ugly both because the monitor is higher resolution and because
  the video is shown frame-after-frame instead of field-after-field.
</para>

<itemizedlist>
<title>Notes:</title>
<listitem><para>
  This section only applies to NTSC DVDs, and not PAL.
  </para></listitem>
<listitem><para>
  The example <application>MEncoder</application> lines throughout the
  document are <emphasis role="bold">not</emphasis> intended for
  actual use. They are simply the bare minimum required to encode the
  pertaining video category. How to make good DVD rips or fine-tune
  <systemitem class="library">libavcodec</systemitem> for maximal
  quality is not within the scope of this document.
  </para></listitem>
<listitem><para>
  There are a couple footnotes specific to this guide, linked like this:
  <link linkend="menc-feat-telecine-footnotes">[1]</link>
  </para></listitem>
</itemizedlist>
</sect2>

<sect2 id="menc-feat-telecine-ident">
<title>How to tell what type of video you have</title>

<sect3 id="menc-feat-telecine-ident-progressive">
<title>Progressive</title>
<para>
  Progressive video was originally filmed at 24000/1001 fps, and stored
  on the DVD without alteration.
</para>

<para>
  When you play a progressive DVD in <application>MPlayer</application>,
  <application>MPlayer</application> will print the following line as
  soon as the movie begins to play:

  <screen> demux_mpg: 24000/1001 fps progressive NTSC content detected, switching framerate.</screen>

  From this point forward, demux_mpg should never say it finds
  &quot;30000/1001 fps NTSC content.&quot;
</para>

<para>
  When you watch progressive video, you should never see any
  interlacing. Beware, however, because sometimes there is a tiny bit
  of telecine mixed in where you would not expect. I have encountered TV
  show DVDs that have one second of telecine at every scene change, or
  at seemingly random places. I once watched a DVD that had a
  progressive first half, and the second half was telecined. If you
  want to be <emphasis>really</emphasis> thorough, you can scan the
  entire movie:

  <screen>mplayer dvd://1 -nosound -vo null -benchmark</screen>

  Using <option>-benchmark</option> makes
  <application>MPlayer</application> play the movie as quickly as it
  possibly can; still, depending on your hardware, it can take a
  while. Every time demux_mpg reports a framerate change, the line
  immediately above will show you the time at which the change
  occurred.
</para>

<para>
  Sometimes progressive video on DVDs is referred to as
  &quot;soft-telecine&quot; because it is intended to
  be telecined by the DVD player.
</para>
</sect3>

<sect3 id="menc-feat-telecine-ident-telecined">
<title>Telecined</title>
<para>
  Telecined video was originally filmed at 24000/1001, but was telecined
  <emphasis>before</emphasis> it was written to the DVD.
</para>

<para>
  <application>MPlayer</application> does not (ever) report any
  framerate changes when it plays telecined video.
</para>

<para>
  Watching a telecined video, you will see interlacing artifacts that
  seem to &quot;blink&quot;: they repeatedly appear and disappear.
  You can look closely at this by
  <orderedlist>
  <listitem>
    <screen>mplayer dvd://1</screen>
    </listitem>
  <listitem><para>
    Seek to a part with motion.
    </para></listitem>
  <listitem><para>
    Use the <keycap>.</keycap> key to step forward one frame at a time.
    </para></listitem>
  <listitem><para>
    Look at the pattern of interlaced-looking and progressive-looking
    frames. If the pattern you see is PPPII,PPPII,PPPII,... then the
    video is telecined. If you see some other pattern, then the video
    may have been telecined using some non-standard method;
    <application>MEncoder</application> cannot losslessly convert
    non-standard telecine to progressive. If you do not see any
    pattern at all, then it is most likely interlaced.
    </para></listitem>
  </orderedlist>
</para>

<para>
  Sometimes telecined video on DVDs is referred to as
  &quot;hard-telecine&quot;. Since hard-telecine is already 60000/1001 fields
  per second, the DVD player plays the video without any manipulation.
</para>

<para>
  Another way to tell if your source is telecined or not is to play
  the source with the <option>-vf pullup</option> and <option>-v</option>
  command line options to see how <option>pullup</option> matches frames.
  If the source is telecined, you should see on the console a 3:2 pattern
  with <systemitem>0+.1.+2</systemitem> and <systemitem>0++1</systemitem>
  alternating.
  This technique has the advantage that you do not need to watch the
  source to identify it, which could be useful if you wish to automate
  the encoding procedure, or to carry out said procedure remotely via
  a slow connection.
</para>

</sect3>

<sect3 id="menc-feat-telecine-ident-interlaced">
<title>Interlaced</title>
<para>
  Interlaced video was originally filmed at 60000/1001 fields per second,
  and stored on the DVD as 30000/1001 frames per second. The interlacing effect
  (often called &quot;combing&quot;) is a result of combining pairs of
  fields into frames. Each field is supposed to be 1/(60000/1001) seconds apart,
  and when they are displayed simultaneously the difference is apparent.
</para>

<para>
  As with telecined video, <application>MPlayer</application> should
  not ever report any framerate changes when playing interlaced content.
</para>

<para>
  When you view an interlaced video closely by frame-stepping with the
  <keycap>.</keycap> key, you will see that every single frame is interlaced.
</para>
</sect3>

<sect3 id="menc-feat-telecine-ident-mixedpt">
<title>Mixed progressive and telecine</title>
<para>
  All of a &quot;mixed progressive and telecine&quot; video was originally
  24000/1001 frames per second, but some parts of it ended up being telecined.
</para>

<para>
  When <application>MPlayer</application> plays this category, it will
  (often repeatedly) switch back and forth between &quot;30000/1001 fps NTSC&quot;
  and &quot;24000/1001 fps progressive NTSC&quot;. Watch the bottom of
  <application>MPlayer</application>'s output to see these messages.
</para>

<para>
  You should check the &quot;30000/1001 fps NTSC&quot; sections to make sure
  they are actually telecine, and not just interlaced.
</para>
</sect3>

<sect3 id="menc-feat-telecine-ident-mixedpi">
<title>Mixed progressive and interlaced</title>
<para>
  In &quot;mixed progressive and interlaced&quot; content, progressive
  and interlaced video have been spliced together.
</para>

<para>
  This category looks just like &quot;mixed progressive and telecine&quot;,
  until you examine the 30000/1001 fps sections and see that they do not have the
  telecine pattern.
</para>
</sect3>

</sect2>

<sect2 id="menc-feat-telecine-encode">
<title>How to encode each category</title>
<para>
  As I mentioned in the beginning, example <application>MEncoder</application>
  lines below are <emphasis role="bold">not</emphasis> meant to actually be used;
  they only demonstrate the minimum parameters to properly encode each category.
</para>

<sect3 id="menc-feat-telecine-encode-progressive">
<title>Progressive</title>
<para>
  Progressive video requires no special filtering to encode. The only
  parameter you need to be sure to use is
  <option>-ofps 24000/1001</option>. Otherwise, <application>MEncoder</application>
  will try to encode at 30000/1001 fps and will duplicate frames.
</para>

<para>
  <screen>mencoder dvd://1 -oac copy -ovc lavc -ofps 24000/1001</screen>
</para>

<para>
  It is often the case, however, that a video that looks progressive
  actually has very short parts of telecine mixed in. Unless you are
  sure, it is safest to treat the video as
  <link linkend="menc-feat-telecine-encode-mixedpt">mixed progressive and telecine</link>.
  The performance loss is small
  <link linkend="menc-feat-telecine-footnotes">[3]</link>.
</para>
</sect3>

<sect3 id="menc-feat-telecine-encode-telecined">
<title>Telecined</title>
<para>
  Telecine can be reversed to retrieve the original 24000/1001 content,
  using a process called inverse-telecine.
  <application>MPlayer</application> contains several filters to
  accomplish this; the best filter, <option>pullup</option>, is described
  in the <link linkend="menc-feat-telecine-encode-mixedpt">mixed
  progressive and telecine</link> section.
</para>
</sect3>

<sect3 id="menc-feat-telecine-encode-interlaced">
<title>Interlaced</title>
<para>
  For most practical cases it is not possible to retrieve a complete
  progressive video from interlaced content. The only way to do so
  without losing half of the vertical resolution is to double the
  framerate and try to &quot;guess&quot; what ought to make up the
  corresponding lines for each field (this has drawbacks - see method
  3).
</para>

<orderedlist>
<listitem><para>

  Encode the video in interlaced form. Normally, interlacing wreaks
  havoc with the encoder's ability to compress well, but
  <systemitem class="library">libavcodec</systemitem> has two
  parameters specifically for dealing with storing interlaced video a
  bit better: <option> ildct</option> and <option>ilme</option>. Also,
  using <option>mbd=2</option> is strongly recommended
  <link linkend="menc-feat-telecine-footnotes">[2] </link> because it
  will encode macroblocks as non-interlaced in places where there is
  no motion. Note that <option>-ofps</option> is NOT needed here.

  <screen>mencoder dvd://1 -oac copy -ovc lavc -lavcopts ildct:ilme:mbd=2</screen>
  </para></listitem>
<listitem><para>
  Use a deinterlacing filter before encoding. There are several of
  these filters available to choose from, each with its own advantages
  and disadvantages. Consult <option>mplayer -pphelp</option> to see
  what is available (grep for &quot;deint&quot;), and search the
  <ulink url="http://www.mplayerhq.hu/homepage/design6/info.html#mailing_lists">
  MPlayer mailing lists</ulink> to find many discussions about the
  various filters. Again, the framerate is not changing, so no
  <option>-ofps</option>. Also, deinterlacing should be done after
  cropping <link linkend="menc-feat-telecine-footnotes">[1]</link> and
  before scaling.

  <screen>mencoder dvd://1 -oac copy -vf pp=lb -ovc lavc</screen>
  </para></listitem>
<listitem><para>
  Unfortunately, this option is buggy with
  <application>MEncoder</application>; it ought to work well with
  <application>MEncoder G2</application>, but that is not here yet. You
  might experience crahes. Anyway, the purpose of <option> -vf
  tfields</option> is to create a full frame out of each field, which
  makes the framerate 60000/1001. The advantage of this approach is that no
  data is ever lost; however, since each frame comes from only one
  field, the missing lines have to be interpolated somehow. There are
  no very good methods of generating the missing data, and so the
  result will look a bit similar to when using some deinterlacing
  filters. Generating the missing lines creates other issues, as well,
  simply because the amount of data doubles. So, higher encoding
  bitrates are required to maintain quality, and more CPU power is
  used for both encoding and decoding. tfields has several different
  options for how to create the missing lines of each frame. If you
  use this method, then Reference the manual, and chose whichever
  option looks best for your material. Note that when using
  <option>tfields</option> you
  <emphasis role="bold">have to</emphasis> specify both
  <option>-fps</option> and <option>-ofps</option> to be twice the
  framerate of your original source.

  <screen>mencoder dvd://1 -oac copy -vf tfields=2 -ovc lavc -fps 60000/1001 -ofps 60000/1001</screen>
  </para></listitem>
<listitem><para>
  If you plan on downscaling dramatically, you can extract and encode
  only one of the two fields. Of course, you will lose half the vertical
  resolution, but if you plan on downscaling to at most 1/2 of the
  original, the loss will not matter much. The result will be a
  progressive 30000/1001 frames per second file. The procedure is to use
  <option>-vf field</option>, then crop
  <link linkend="menc-feat-telecine-footnotes">[1]</link> and scale
  appropriately. Remember that you will have to adjust the scale to
  compensate for the vertical resolution being halved.
  <screen>mencoder dvd://1 -oac copy -vf field=0 -ovc lavc</screen>
  </para></listitem>
</orderedlist>
</sect3>

<sect3 id="menc-feat-telecine-encode-mixedpt">
<title>Mixed progressive and telecine</title>
<para>
  In order to turn mixed progressive and telecine video into entirely
  progressive video, the telecined parts have to be
  inverse-telecined. There are three ways to accomplish this,
  described below. Note that you should
  <emphasis role="bold">always</emphasis> inverse-telecine before any
  rescaling; unless you really know what you are doing,
  inverse-telecine before cropping, too
  <link linkend="menc-feat-telecine-footnotes">[1]</link>.
  <option>-ofps 24000/1001</option> is needed here because the output video
  will be 24000/1001 frames per second.
</para>

<itemizedlist>
<listitem><para>
  <option>-vf pullup</option> is designed to inverse-telecine
  telecined material while leaving progressive data alone. In order to
  work properly, <option>pullup</option> <emphasis role="bold">must</emphasis>
  be followed by the <option>softskip</option> filter or
  else <application>MEncoder</application> will crash.
  <option>pullup</option> is, however, the cleanest and most
  accurate method available for encoding both telecine and
  &quot;mixed progressive and telecine&quot;.

  <screen>mencoder dvd://1 -oac copy -vf pullup,softskip -ovc lavc -ofps 24000/1001</screen>
  </para>


  </listitem>
  <listitem><para>
  An older method
  is to, rather than inverse-telecine the telecined parts, telecine
  the non-telecined parts and then inverse-telecine the whole
  video. Sound confusing? softpulldown is a filter that goes through
  a video and makes the entire file telecined. If we follow
  softpulldown with either <option>detc</option> or
  <option>ivtc</option>, the final result will be entirely
  progressive. <option>-ofps 24000/1001</option> is needed.

  <screen>mencoder dvd://1 -oac copy -vf softpulldown,ivtc=1 -ovc lavc -ofps 24000/1001</screen>
  </para>
  </listitem>

<listitem><para>
  I have not used <option>-vf filmdint</option> myself, but here is what
  D Richard Felker III has to say:

  <blockquote><para>It is OK, but IMO it tries to deinterlace rather
    than doing inverse telecine too often (much like settop DVD
    players &amp; progressive TVs) which gives ugly flickering and
    other artifacts. If you are going to use it, you at least need to
    spend some time tuning the options and watching the output first
    to make sure it is not messing up.</para></blockquote>
  </para></listitem>
</itemizedlist>
</sect3>

<sect3 id="menc-feat-telecine-encode-mixedpi">
<title>Mixed progressive and interlaced</title>
<para>
  There are two options for dealing with this category, each of
  which is a compromise. You should decide based on the
  duration/location of each type.
</para>

<itemizedlist>
<listitem><para>
  Treat it as progressive. The interlaced parts will look interlaced,
  and some of the interlaced fields will have to be dropped, resulting
  in a bit of uneven jumpiness. You can use a postprocessing filter if
  you want to, but it may slightly degrade the progressive parts.
  </para>

  <para>
  This option should definitely not be used if you want to eventually
  display the video on an interlaced device (with a TV card, for
  example). If you have interlaced frames in a 24000/1001 frames per
  second video, they will be telecined along with the progressive
  frames. Half of the interlaced "frames" will be displayed for three
  fields' duration (3/(60000/1001) seconds), resulting in a flicking
  &quot;jump back in time&quot; effect that looks quite bad. If you
  even attempt this, you <emphasis role="bold">must</emphasis> use a
  deinterlacing filter like <option>lb</option> or
  <option>l5</option>.
  </para>

  <para>
  It may also be a bad idea for progressive display, too. It will drop
  pairs of consecutive interlaced fields, resulting in a discontinuity
  that can be more visible than with the second method, which shows
  some progressive frames twice. 30000/1001 frames per second interlaced
  video is already a bit choppy because it really should be shown at
  60000/1001 fields per second, so the duplicate frames do not stand out as
  much.
  </para>

  <para>
  Either way, it is best to consider your content and how you intend to
  display it. If your video is 90% progressive and you never intend to
  show it on a TV, you should favor a progressive approach. If it is
  only half progressive, you probably want to encode it as if it is all
  interlaced.
  </para>
  </listitem>

<listitem><para>
  Treat it as interlaced. Some frames of the progressive parts will
  need to be duplicated, resulting in uneven jumpiness. Again,
  deinterlacing filters may slightly degrade the progressive parts.
  </para></listitem>

</itemizedlist>
</sect3>

</sect2>

<sect2 id="menc-feat-telecine-footnotes">
<title>Footnotes</title>
<orderedlist>
<listitem><formalpara>
  <title>About cropping:</title>
  <para>
  Video data on DVDs are stored in a format called YUV 4:2:0. In YUV
  video, luma (&quot;brightness&quot;) and chroma (&quot;color&quot;)
  are stored separately. Because the human eye is somewhat less
  sensitive to color than it is to brightness, in a YUV 4:2:0 picture
  there is only one chroma pixel for every four luma pixels. In a
  progressive picture, each square of four luma pixels (two on each
  side) has one common chroma pixel. You must crop progressive YUV
  4:2:0 to even resolutions, and use even offsets. For example,
  <option>crop=716:380:2:26</option> is OK but
  <option>crop=716:380:3:26 </option> is not.
  </para>
  </formalpara>

  <para>
  When you are dealing with interlaced YUV 4:2:0, the situation is a
  bit more complicated. Instead of every four luma pixels in the
  <emphasis>frame</emphasis> sharing a chroma pixel, every four luma
  pixels in each <emphasis> field</emphasis> share a chroma
  pixel. When fields are interlaced to form a frame, each scanline is
  one pixel high. Now, instead of all four luma pixels being in a
  square, there are two pixels side-by-side, and the other two pixels
  are side-by-side two scanlines down. The two luma pixels in the
  intermediate scanline are from the other field, and so share a
  different chroma pixel with two luma pixels two scanlines away. All
  this confusion makes it necessary to have vertical crop dimensions
  and offsets be multiples of four. Horizontal can stay even.
  </para>

  <para>
  For telecined video, I recommend that cropping take place after
  inverse telecining. Once the video is progressive you only need to
  crop by even numbers. If you really want to gain the slight speedup
  that cropping first may offer, you must crop vertically by multiples
  of four or else the inverse-telecine filter will not have proper data.
  </para>

  <para>
  For interlaced (not telecined) video, you must always crop
  vertically by multiples of four unless you use <option>-vf
  field</option> before cropping.
  </para>
  </listitem>

<listitem><formalpara>
  <title>About encoding parameters and quality:</title>
  <para>
  Just because I recommend <option>mbd=2</option> here does not mean it
  should not be used elsewhere. Along with <option>trell</option>,
  <option>mbd=2</option> is one of the two
   <systemitem class="library">libavcodec</systemitem> options that
  increases quality the most, and you should always use at least those
  two unless the drop in encoding speed is prohibitive (e.g. realtime
  encoding). There are many other options to
  <systemitem class="library">libavcodec</systemitem> that increase
  encoding quality (and decrease encoding speed) but that is beyond
  the scope of this document.
  </para>
  </formalpara>
  </listitem>

<listitem><formalpara>
  <title>About the performance of pullup:</title>
  <para>
  It is safe to use <option>pullup</option> (along with <option>softskip
  </option>) on progressive video, and is usually a good idea unless
  the source has been definitively verified to be entirely progressive.
  The performace loss is small for most cases. On a bare-minimum encode,
  <option>pullup</option> causes <application>MEncoder</application> to
  be 50% slower. Adding sound processing and advanced <option>lavcopts
  </option> overshadows that difference, bringing the performance
  decrease of using <option>pullup</option> down to 2%.
  </para>
  </formalpara>
  </listitem>

</orderedlist>

</sect2>

</sect1>


<sect1 id="menc-feat-enc-libavcodec">
<title>Encoding with the <systemitem class="library">libavcodec</systemitem>
  codec family</title>

<para>
<link linkend="ffmpeg"><systemitem class="library">libavcodec</systemitem></link>
provides simple encoding to a lot of interesting video and audio formats.
You can encode to the following codecs (more or less up to date):
</para>

<sect2 id="menc-feat-enc-libavcodec-video-codecs">
<title><systemitem class="library">libavcodec</systemitem>'s video codecs</title>

<para>
<informaltable frame="all">
<tgroup cols="2">
<thead>
<row><entry>Video codec name</entry><entry>Description</entry></row>
</thead>
<tbody>
<row><entry>mjpeg</entry><entry>
   Motion JPEG
  </entry></row>
<row><entry>ljpeg</entry><entry>
   lossless JPEG
  </entry></row>
<row><entry>h261</entry><entry>
  H.261
  </entry></row>
<row><entry>h263</entry><entry>
  H.263
  </entry></row>
<row><entry>h263p</entry><entry>
  H.263+
  </entry></row>
<row><entry>mpeg4</entry><entry>
  ISO standard MPEG-4 (DivX 5, XviD compatible)
  </entry></row>
<row><entry>msmpeg4</entry><entry>
  pre-standard MPEG-4 variant by MS, v3 (AKA DivX3)
  </entry></row>
<row><entry>msmpeg4v2</entry><entry>
  pre-standard MPEG-4 by MS, v2 (used in old ASF files)
  </entry></row>
<row><entry>wmv1</entry><entry>
  Windows Media Video, version 1 (AKA WMV7)
  </entry></row>
<row><entry>wmv2</entry><entry>
  Windows Media Video, version 2 (AKA WMV8)
  </entry></row>
<row><entry>rv10</entry><entry>
  RealVideo 1.0
  </entry></row>
<row><entry>rv20</entry><entry>
  RealVideo 2.0
  </entry></row>
<row><entry>mpeg1video</entry><entry>
  MPEG-1 video
  </entry></row>
<row><entry>mpeg2video</entry><entry>
  MPEG-2 video
  </entry></row>
<row><entry>huffyuv</entry><entry>
  lossless compression
  </entry></row>
<row><entry>asv1</entry><entry>
  ASUS Video v1
  </entry></row>
<row><entry>asv2</entry><entry>
  ASUS Video v2
  </entry></row>
<row><entry>ffv1</entry><entry>
  FFmpeg's lossless video codec
  </entry></row>
<row><entry>svq1</entry><entry>
  Sorenson video 1
  </entry></row>
<row><entry>flv</entry><entry>
  Sorenson H.263 used in Flash Video
  </entry></row>
<row><entry>dvvideo</entry><entry>
  Sony Digital Video
  </entry></row>
<row><entry>snow</entry><entry>
  FFmpeg's experimental wavelet-based codec
  </entry></row>
</tbody>
</tgroup>
</informaltable>

The first column contains the codec names that should be passed after the
<literal>vcodec</literal> config, like: <option>-lavcopts vcodec=msmpeg4</option>
</para>
<informalexample>
<para>
An example with MJPEG compression:
<screen>mencoder dvd://2 -o title2.avi -ovc lavc -lavcopts vcodec=mjpeg -oac copy</screen>
</para>
</informalexample>
</sect2>

<sect2 id="menc-feat-enc-libavcodec-audio-codecs">
<title><systemitem class="library">libavcodec</systemitem>'s audio codecs</title>
<para>
<informaltable frame="all">
<tgroup cols="2">
<thead>
<row><entry>Audio codec name</entry><entry>Description</entry></row>
</thead>
<tbody>
  <row>
    <entry>mp2</entry>
    <entry>MPEG Layer 2</entry>
  </row>
  <row>
    <entry>ac3</entry>
    <entry>AC3, AKA Dolby Digital</entry>
  </row>
  <row>
    <entry>adpcm_ima_wav</entry>
    <entry>IMA adaptive PCM (4 bits per sample, 4:1 compression)</entry>
  </row>
  <row>
    <entry>sonic</entry>
    <entry>experimental lossy/lossless codec</entry>
  </row>
</tbody>
</tgroup>
</informaltable>

The first column contains the codec names that should be passed after the
<literal>acodec</literal> option, like: <option>-lavcopts acodec=ac3</option>
</para>

<informalexample>
<para>
An example with AC3 compression:
<screen>mencoder dvd://2 -o title2.avi -oac lavc -lavcopts acodec=ac3 -ovc copy</screen>
</para>
</informalexample>

<para>
  Contrary to <systemitem class="library">libavcodec</systemitem>'s video
  codecs, its audio codecs do not make a wise usage of the bits they are
  given as they lack some minimal psychoacoustic model (if at all)
  which most other codec implementations feature.
  However, note that all these audio codecs are very fast and work
  out-of-the-box everywhere <application>MEncoder</application> has been
  compiled with <systemitem class="library">libavcodec</systemitem> (which
  is the case most of time), and do not depend on external libraries.
</para>
</sect2>


<sect2 id="menc-feat-dvd-mpeg4-lavc-encoding-options">
<title>Encoding options of libavcodec</title>

<para>
  Ideally, you would probably want to be able to just tell the encoder to switch
  into "high quality" mode and move on.
  That would probably be nice, but unfortunately hard to implement as different
  encoding options yield different quality results depending on the source material.
  That is because compression depends on the visual properties of the video
  in question.
  For example, anime and live action have very different properties and
  thus require different options to obtain optimum encoding.
  The good news is that some options should never be left out, like
  <option>mbd=2</option>, <option>trell</option>, and <option>v4mv</option>.
  See below for a detailed description of common encoding options.
</para>


<itemizedlist>
<title>Options to adjust:</title>
<listitem><para>
  <emphasis role="bold">vmax_b_frames</emphasis>: 1 or 2 is good, depending on
  the movie.
  Note that if you need to have your encode be decodable by DivX5, you
  need to activate closed GOP support, using
  <systemitem class="library">libavcodec</systemitem>'s <option>cgop</option>
  option, but you need to deactivate scene detection, which
  is not a good idea as it will hurt encode efficiency a bit.
</para></listitem>

<listitem><para>
  <emphasis role="bold">vb_strategy=1</emphasis>: helps in high-motion scenes.
  On some videos, vmax_b_frames may hurt quality, but vmax_b_frames=2 along
  with vb_strategy=1 helps.
</para></listitem>

<listitem><para>
  <emphasis role="bold">dia</emphasis>: motion search range. Bigger is better
  and slower.
  Negative values are a completely different scale.
  Good values are -1 for a fast encode, or 2-4 for slower.
</para></listitem>

<listitem><para>
  <emphasis role="bold">predia</emphasis>: motion search pre-pass.
  Not as important as dia. Good values are 1 (default) to 4. Requires preme=2
  to really be useful.
</para></listitem>

<listitem><para>
  <emphasis role="bold">cmp, subcmp, precmp</emphasis>: Comparison function for
  motion estimation.
  Experiment with values of 0 (default), 2 (hadamard), 3 (dct), and 6 (rate
  distortion).
  0 is fastest, and sufficient for precmp.
  For cmp and subcmp, 2 is good for anime, and 3 is good for live action.
  6 may or may not be slightly better, but is slow.
</para></listitem>

<listitem><para>
  <emphasis role="bold">last_pred</emphasis>: Number of motion predictors to
  take from the previous frame.
  1-3 or so help at little speed cost.
  Higher values are slow for no extra gain.
</para></listitem>

<listitem><para>
  <emphasis role="bold">cbp, mv0</emphasis>: Controls the selection of macroblocks.
  Small speed cost for small quality gain.
</para></listitem>

<listitem><para>
  <emphasis role="bold">qprd</emphasis>: adaptive quantization based on the
  macroblock's complexity.
  May help or hurt depending on the video and other options.
  This can cause artifacts unless you set vqmax to some reasonably small value
  (6 is good, maybe as low as 4); vqmin=1 should also help.
</para></listitem>

<listitem><para>
  <emphasis role="bold">qns</emphasis>: very slow, especially when combined
  with qprd.
  This option will make the encoder minimize noise due to compression
  artifacts instead of making the encoded video strictly match the source.
  Do not use this unless you have already tweaked everything else as far as it
  will go and the results still are not good enough.
</para></listitem>

<listitem><para>
  <emphasis role="bold">vqcomp</emphasis>: Tweak ratecontrol.
  What values are good depends on the movie.
  You can safely leave this alone if you want.
  Reducing vqcomp puts more bits on low-complexity scenes, increasing it puts
  them on high-complexity scenes (default: 0.5, range: 0-1. recommended range:
  0.5-0.7).
</para></listitem>

<listitem><para>
  <emphasis role="bold">vlelim, vcelim</emphasis>: Sets the single coefficient
  elimination threshold for luminance and chroma planes.
  These are encoded separately in all MPEG-like algorithms.
  The idea behind these options is to use some good heuristics to determine
  when the change in a block is less than the threshold you specify, and in
  such a case, to just  encode the block as "no change".
  This saves bits and perhaps speeds up encoding. vlelim=-4 and vcelim=9
  seem to be good for live movies, but seem not to help with anime;
  when encoding animation, you should probably leave them unchanged.
</para></listitem>

<listitem><para>
  <emphasis role="bold">qpel</emphasis>: Quarter pixel motion estimation.
  MPEG-4 uses half pixel precision for its motion search by default,
  therefore this option comes with an overhead as more information will be
  stored in the encoded file.
  The compression gain/loss depends on the movie, but it is usually not very
  effective on anime.
  qpel always incurs a significant cost in CPU decode time (+25% in
  practice).
</para></listitem>

<listitem><para>
  <emphasis role="bold">psnr</emphasis>: does not affect the actual encoding,
  but writes a log file giving the type/size/quality of each frame, and
  prints a summary of PSNR (Peak Signal to Noise Ratio) at the end.
</para></listitem>

</itemizedlist>

<itemizedlist>
<title>Options not recommended to play with:</title>
<listitem><para>
  <emphasis role="bold">vme</emphasis>: The default is best.
</para></listitem>

<listitem><para>
  <emphasis role="bold">lumi_mask, dark_mask</emphasis>: Psychovisual adaptive
  quantization.
  You do not want to play with those options if you care about quality.
  Reasonable values may be effective in your case, but be warned this is very
  subjective.
</para></listitem>

<listitem><para>
  <emphasis role="bold">scplx_mask</emphasis>: Tries to prevent blocky
  artifacts, but postprocessing is better.
</para></listitem>
</itemizedlist>
</sect2>

<sect2 id="menc-feat-mpeg4-lavc-example-settings">
<title>Encoding setting examples</title>

<para>
  The following settings are examples of different encoding
  option combinations that affect the speed vs quality tradeoff
  at the same target bitrate.
</para>

<para>
  All the encoding settings were tested on a 720x448 @30000/1001 fps
  video sample, the target bitrate was 900kbps, and the machine was an
  AMD-64 3400+ at 2400 Mhz in 64 bits mode.
  Each encoding setting features the measured encoding speed (in
  frames per second) and the PSNR loss (in dB) compared to the "very
  high quality" setting.
  Please understand that depending on your source, your machine type
  and development advancements, you may get very different results.
</para>

<para>
<informaltable frame="all">
<tgroup cols="4">
<thead>
<row><entry>Description</entry><entry>Encoding options</entry><entry>speed (in fps)</entry><entry>Relative PSNR loss (in dB)</entry></row>
</thead>
<tbody>
<row>
  <entry>Very high quality</entry>
  <entry><option>vcodec=mpeg4:mbd=2:mv0:trell:v4mv:cbp:last_pred=3:predia=2:dia=2:vmax_b_frames=2:vb_strategy=1:precmp=2:cmp=2:subcmp=2:preme=2:vme=5:naq:qns=2</option></entry>
  <entry>6fps</entry>
  <entry>0dB</entry>
</row>
<row>
  <entry>High quality</entry>
  <entry><option>vcodec=mpeg4:mbd=2:trell:v4mv:last_pred=2:dia=-1:vmax_b_frames=2:vb_strategy=1:cmp=3:subcmp=3:precmp=0:vqcomp=0.6:turbo</option></entry>
  <entry>15fps</entry>
  <entry>-0.5dB</entry>
</row>
<row>
  <entry>Fast</entry>
  <entry><option>vcodec=mpeg4:mbd=2:trell:v4mv:turbo</option></entry>
  <entry>42fps</entry>
  <entry>-0.74dB</entry>
</row>
<row>
  <entry>Realtime</entry>
  <entry><option>vcodec=mpeg4:mbd=2:turbo</option></entry>
  <entry>54fps</entry>
  <entry>-1.21dB</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</para>
</sect2>

<sect2 id="custommatrices"><title>Custom inter/intra matrices</title>

<para>
With this feature of
<link linkend="ffmpeg"><systemitem class="library">libavcodec</systemitem></link>
you are able to set custom inter (I-frames/keyframes) and intra
(P-frames/predicted frames) matrices. It is supported by many of the codecs:
<systemitem>mpeg1video</systemitem> and <systemitem>mpeg2video</systemitem>
are reported as working.
</para>

<para>
A typical usage of this feature is to set the matrices preferred by the
<ulink url="http://www.kvcd.net/">KVCD</ulink> specifications.
</para>

<para>
The <emphasis role="bold">KVCD &quot;Notch&quot; Quantization Matrix:</emphasis>
</para>

<para>
Intra:
<screen>
 8  9 12 22 26 27 29 34
 9 10 14 26 27 29 34 37
12 14 18 27 29 34 37 38
22 26 27 31 36 37 38 40
26 27 29 36 39 38 40 48
27 29 34 37 38 40 48 58
29 34 37 38 40 48 58 69
34 37 38 40 48 58 69 79
</screen>

Inter:
<screen>
16 18 20 22 24 26 28 30
18 20 22 24 26 28 30 32
20 22 24 26 28 30 32 34
22 24 26 30 32 32 34 36
24 26 28 32 34 34 36 38
26 28 30 32 34 36 38 40
28 30 32 34 36 38 42 42
30 32 34 36 38 40 42 44
</screen>
</para>

<para>
Usage:
<screen>
$ mencoder <replaceable>input.avi</replaceable> -o <replaceable>output.avi</replaceable> -oac copy -ovc lavc -lavcopts inter_matrix=...:intra_matrix=...
</screen>
</para>

<para>
<screen>
$ mencoder <replaceable>input.avi</replaceable> -ovc lavc -lavcopts
vcodec=mpeg2video:intra_matrix=8,9,12,22,26,27,29,34,9,10,14,26,27,29,34,37,
12,14,18,27,29,34,37,38,22,26,27,31,36,37,38,40,26,27,29,36,39,38,40,48,27,
29,34,37,38,40,48,58,29,34,37,38,40,48,58,69,34,37,38,40,48,58,69,79
:inter_matrix=16,18,20,22,24,26,28,30,18,20,22,24,26,28,30,32,20,22,24,26,
28,30,32,34,22,24,26,30,32,32,34,36,24,26,28,32,34,34,36,38,26,28,30,32,34,
36,38,40,28,30,32,34,36,38,42,42,30,32,34,36,38,40,42,44 -oac copy -o svcd.mpg
</screen>
</para>
</sect2>


<sect2 id="menc-feat-dvd-mpeg4-example">
<title>Example</title>

<para>
  So, you have just bought your shiny new copy of Harry Potter and the Chamber
  of Secrets (widescreen edition, of course), and you want to rip this DVD
  so that you can add it to your Home Theatre PC. This is a region 1 DVD,
  so it is NTSC. The example below will still apply to PAL, except you will
  omit <option>-ofps 24000/1001</option> (because the output framerate is the
  same as the input framerate), and of course the crop dimensions will be
  different.
</para>

<para>
  After running <option>mplayer dvd://1</option>, we follow the process
  detailed in the section <link linkend="menc-feat-telecine">How to deal
  with telecine and interlacing in NTSC DVDs</link> and discover that it is
  24000/1001 fps progressive video, which means that we need not use an inverse
  telecine filter, such as <option>pullup</option> or
  <option>filmdint</option>.
</para>

<para>
  Next, we want to determine the appropriate crop rectangle, so we use the
  cropdetect filter:

  <screen>mplayer dvd://1 -vf cropdetect</screen>

  Make sure you seek to a fully filled frame (such as a bright scene), and
  you will see in <application>MPlayer</application>'s console output:

  <screen>crop area: X: 0..719  Y: 57..419  (-vf crop=720:362:0:58)</screen>

  We then play the movie back with this filter to test its correctness:

  <screen>mplayer dvd://1 -vf crop=720:362:0:58</screen>

  And we see that it looks perfectly fine. Next, we ensure the width and
  height are a multiple of 16. The width is fine, however the height is
  not. Since we did not fail 7th grade math, we know that the nearest
  multiple of 16 lower than 362 is 352.
</para>

<para>
  We could just use <option>crop=720:352:0:58</option>, but it would be nice
  to take a little off the top and a little off the bottom so that we
  retain the center. We have shrunk the height by 10 pixels, but we do not
  want to increase the y-offset by 5-pixels since that is an odd number and
  will adversely affect quality. Instead, we will increase the y-offset by
  4 pixels:

  <screen>mplayer dvd://1 -vf crop=720:352:0:62</screen>

  Another reason to shave pixels from both the top and the bottom is that we
  ensure we have eliminated any half-black pixels if they exist. Note that if
  your video is telecined, make sure the <option>pullup</option> filter (or
  whichever inverse telecine filter you decide to use) appears in the filter
  chain before you crop. If it is interlaced, deinterlace before cropping.
  (If you choose to preserve the interlaced video, then make sure your
  vertical crop offset is a multiple of 4.)
</para>

<para>
  If you are really concerned about losing those 10 pixels, you might
  prefer instead to scale the dimensions down to the nearest multiple of 16.
  The filter chain would look like:

  <screen>-vf crop=720:362:0:58,scale=720:352</screen>

  Scaling the video down like this will mean that some small amount of
  detail is lost, though it probably will not be perceptible. Scaling up will
  result in lower quality (unless you increase the bitrate). Cropping
  discards those pixels altogether. It is a tradeoff that you will want to
  consider for each circumstance. For example, if the DVD video was made
  for television, you might want to avoid vertical scaling, since the line
  sampling corresponds to the way the content was originally recorded.
</para>

<para>
  On inspection, we see that our movie has a fair bit of action and high
  amounts of detail, so we pick 2400Kbit for our bitrate.
</para>

<para>
  We are now ready to do the two pass encode. Pass one:

  <screen>mencoder dvd://1 -ofps 24000/1001 -oac copy -vf crop=720:352:0:62,hqdn3d=2:1:2 -ovc lavc \
-lavcopts vcodec=mpeg4:vbitrate=2400:v4mv:mbd=2:trell:cmp=3:subcmp=3:mbcmp=3:autoaspect:vpass=1 \
-o Harry_Potter_2.avi</screen>

  And pass two is the same, except that we specify <option>vpass=2</option>:

  <screen>mencoder dvd://1 -ofps 24000/1001 -oac copy -vf crop=720:352:0:62,hqdn3d=2:1:2 -ovc lavc \
-lavcopts vcodec=mpeg4:vbitrate=2400:v4mv:mbd=2:trell:cmp=3:subcmp=3:mbcmp=3:autoaspect:vpass=2 \
-o Harry_Potter_2.avi</screen>
</para>

<para>
  The options <option>v4mv:mbd=2:trell</option> will greatly increase the
  quality at the expense of encoding time. There is little reason to leave
  these options out when the primary goal is quality. The options
  <option>cmp=3:subcmp=3:mbcmp=3</option> select a comparison function that
  yields higher quality than the defaults. You might try experimenting with
  this parameter (refer to the man page for the possible values) as
  different functions can have a large impact on quality depending on the
  source material. For example, if you find
  <systemitem class="library">libavcodec</systemitem> produces too much
  blocky artifacting, you could try selecting the experimental NSSE as
  comparison function via <option>*cmp=10</option>.
</para>

<para>
  For this movie, the resulting AVI will be 138 minutes long and nearly
  3GB. And because you said that file size does not matter, this is a
  perfectly acceptable size. However, if you had wanted it smaller, you
  could try a lower bitrate. Increasing bitrates have diminishing
  returns, so while we might clearly see an improvement from 1800Kbit to
  2000Kbit, it might not be so noticeable above 2000Kbit. Feel
  free to experiment until you are happy.
</para>

<para>
  Because we passed the source video through a denoise filter, you may want
  to add some of it back during playback. This, along with the
  <option>spp</option> post-processing filter, drastically improves the
  perception of quality and helps eliminate blocky artifacts in the video.
  With <application>MPlayer</application>'s <option>autoq</option> option,
  you can vary the amount of post-processing done by the spp filter
  depending on available CPU. Also, at this point, you may want to apply
  gamma and/or color correction to best suit your display. For example:

  <screen>mplayer Harry_Potter_2.avi -vf spp,noise=9ah:5ah,eq2=1.2 -autoq 3</screen>

</para>
</sect2>
</sect1>


<sect1 id="menc-feat-xvid">
<title>Encoding with the <systemitem class="library">XviD</systemitem>
codec</title>
<para>
 <systemitem class="library">XviD</systemitem> is a free library for
 encoding MPEG-4 ASP video streams.
 Before starting to encode, you need to <link linkend="xvid">
 set up <application>MEncoder</application> to support it</link>.
</para>
<para>
 This guide mainly aims at featuring the same kind of information
 as x264's encoding guide.
 Therefore, please begin by reading
 <link linkend="menc-feat-x264-encoding-options-intro">the first part</link>
 of that guide.
</para>


<sect2 id="menc-feat-xvid-intro">
<title>What options should I use to get the best results?</title>

<para>
 Please begin by reviewing the
 <systemitem class="library">XviD</systemitem> section of
 <application>MPlayer</application>'s man page.
 This section is intended to be a supplement to the man page.
</para>
<para>
 The XviD default settings are already a good tradeoff between
 speed and quality, therefore you can safely stick to them if
 the following section puzzles you.
</para>
</sect2>

<sect2 id="menc-feat-xvid-encoding-options">
<title>Encoding options of <systemitem class="library">XviD</systemitem></title>

<itemizedlist>
<listitem><para>
 <emphasis role="bold">vhq</emphasis>
  This setting affects the macroblock decision algorithm, where the
  higher the setting, the wiser the decision.
  The default setting may be safely used for every encode, while
  higher settings always help PSNR but are significantly slower.
  Please note that a better PSNR does not necessarily mean
  that the picture will look better, but tells you that it is
  closer to the original.
  Turning it off will noticeably speed up encoding; if speed is
  critical for you, the tradeoff may be worth it.
</para></listitem>

<listitem><para>
 <emphasis role="bold">bvhq</emphasis>
  This does the same job as vhq, but does it on B-frames.
  It has a negligible impact on speed, and slightly improves quality
  (around +0.1dB PSNR).
</para></listitem>

<listitem><para>
 <emphasis role="bold">max_bframes</emphasis>
  A higher number of consecutive allowed B-frames usually improves
  compressibility, although it may also lead to more blocking artifacts.
  The default setting is a good tradeoff between compressibility and
  quality, but you may increase it up to 3 if you are bitrate-starved.
  You may also decrease it to 1 or 0 if you are aiming at perfect
  quality, though in that case you should make sure your
  target bitrate is high enough to ensure that the encoder does not
  have to increase quantizers to reach it.
</para></listitem>

<listitem><para>
 <emphasis role="bold">bf_threshold</emphasis>
  This controls the B-frame sensitivity of the encoder, where a higher
  value leads to more B-frames being used (and vice versa).
  This setting is to be used together with <option>max_bframes</option>;
  if you are bitrate-starved, you should increase both
  <option>max_bframes</option> and <option>bf_threshold</option>,
  while you may increase <option>max_bframes</option> and reduce
  <option>bf_threshold</option> so that the encoder may use more
  B-frames in places that only <emphasis role="bold">really</emphasis>
  need them.
  A low number of <option>max_bframes</option> and a high value of
  <option>bf_threshold</option> is probably not a wise choice as it
  will force the encoder to put B-frames in places that would not
  benefit from them, therefore reducing visual quality.
  However, if you need to be compatible with standalone players that
  only support old DivX profiles (which only supports up to 1
  consecutive B-frame), this would be your only way to
  increase compressibility through using B-frames.
</para></listitem>

<listitem><para>
 <emphasis role="bold">trellis</emphasis>
  Optimizes the quantization process to get an optimal tradeoff
  between PSNR and bitrate, which allows significant bit saving.
  These bits will in return be spent elsewhere on the video,
  raising overall visual quality.
  You should always leave it on as its impact on quality is huge.
  Even if you are looking for speed, do not disable it until you
  have turned down <option>vhq</option> and all other more
  CPU-hungry options to the minimum.
</para></listitem>

<listitem><para>
  <emphasis role="bold">hq_ac</emphasis>
  Activates a better coefficient cost estimation method, which slightly
  reduces filesize by around 0.15 to 0.19% (which corresponds to less
  than 0.01dB PSNR increase), while having a negligible impact on speed.
  It is therefore recommended to always leave it on.
</para></listitem>

<listitem><para>
 <emphasis role="bold">cartoon</emphasis>
  Designed to better encode cartoon content, and has no impact on
  speed as it just tunes the mode decision heuristics for this type
  of content.
</para></listitem>

<listitem><para>
 <emphasis role="bold">me_quality</emphasis>
  This setting is to control the precision of the motion estimation.
  The higher <option>me_quality</option>, the more
  precise the estimation of the original motion will be, and the
  better the resulting clip will capture the original motion.
 </para>
 <para>
  The default setting is best in all cases;
  thus it is not recommended to turn it down unless you are
  really looking for speed, as all the bits saved by a good motion
  estimation would be spent elsewhere, raising overall quality.
  Therefore, do not go any lower than 5, and even that only as a last
  resort.
</para></listitem>

<listitem><para>
 <emphasis role="bold">chroma_me</emphasis>
  Improves motion estimation by also taking the chroma (color)
  information into account, whereas <option>me_quality</option>
  alone only uses luma (grayscale).
  This slows down encoding by 5-10% but improves visual quality
  quite a bit by reducing blocking effects and reduces filesize by
  around 1.3%.
  If you are looking for speed, you should disable this option before
  starting to consider reducing <option>me_quality</option>.
</para></listitem>

<listitem><para>
  <emphasis role="bold">chroma_opt</emphasis>
    Is intended to increase chroma image quality around pure
    white/black edges, rather than improving compression.
    This can help to reduce the "red stairs" effect.
</para></listitem>

<listitem><para>
  <emphasis role="bold">lumi_mask</emphasis>
    Tries to give less bitrate to part of the picture that the
    human eye cannot see very well, which should allow the encoder
    to spend the saved bits on more important parts of the picture.
    The quality of the encode yielded by this option highly depends
    on personal preferences and on the type and monitor settings
    used to watch it (typically, it will not look as good if it is
    bright or if it is a TFT monitor).
</para></listitem>

<listitem><para>
  <emphasis role="bold">qpel</emphasis>
    Raise the number of candidate motion vectors by increasing
    the precision of the motion estimation from halfpel to
    quarterpel.
    The idea is to find better motion vectors which will in return
    reduce bitrate (hence increasing quality).
    However, motion vectors with quarterpel precision require a
    few extra bits to code, but the candidate vectors do not always
    give (much) better results.
    Quite often, the codec still spends bits on the extra precision,
    but little or no extra quality is gained in return.
    Unfortunately, there is no way to foresee the possible gains of
    <option>qpel</option>, so you need to actually encode with and
    without it to know for sure.
  </para><para>
    <option>qpel</option> can be almost double encoding time, and
    requires as much as 25% more processing power to decode.
    It is not supported by all standalone players.
</para></listitem>

<listitem><para>
  <emphasis role="bold">gmc</emphasis>
    Tries to save bits on panning scenes by using a single motion
    vector for the whole frame.
    This almost always raises PSNR, but significantly slows down
    encoding (as well as decoding).
    Therefore, you should only use it when you have turned
    <option>vhq</option> to the maximum.
    <systemitem class="library">XviD</systemitem>'s GMC is more
    sophisticated than DivX's, but is only supported by few
    standalone players.
</para></listitem>

</itemizedlist>
</sect2>

<sect2 id="menc-feat-xvid-encoding-profiles">
<title>Encoding profiles</title>
<para>
  XviD supports encoding profiles through the <option>profile</option> option,
  which are used to impose restrictions on the properties of the XviD video
  stream such that it will be playable on anything which supports the
  chosen profile.
  The restrictions relate to resolutions, bitrates and certain MPEG-4
  features.
  The following table shows what each profile supports.
</para>
<informaltable>
<tgroup cols="16" align="center">
<colspec colnum="1"  colname="col1"/>
<colspec colnum="2"  colname="col2"/>
<colspec colnum="3"  colname="col3"/>
<colspec colnum="4"  colname="col4"/>
<colspec colnum="5"  colname="col5"/>
<colspec colnum="6"  colname="col6"/>
<colspec colnum="7"  colname="col7"/>
<colspec colnum="8"  colname="col8"/>
<colspec colnum="9"  colname="col9"/>
<colspec colnum="10" colname="col10"/>
<colspec colnum="11" colname="col11"/>
<colspec colnum="12" colname="col12"/>
<colspec colnum="13" colname="col13"/>
<colspec colnum="14" colname="col14"/>
<colspec colnum="15" colname="col15"/>
<colspec colnum="16" colname="col16"/>
<colspec colnum="17" colname="col17"/>
<spanspec spanname="spa2-5"   namest="col2" nameend="col5"/>
<spanspec spanname="spa6-11"  namest="col6" nameend="col11"/>
<spanspec spanname="spa12-17" namest="col12" nameend="col17"/>
  <tbody>
    <row>
      <entry></entry>
      <entry spanname="spa2-5">Simple</entry>
      <entry spanname="spa6-11">Advanced Simple</entry>
      <entry spanname="spa12-17">DivX</entry>
    </row>
    <row>
      <entry>Profile name</entry>
      <entry>0</entry>
      <entry>1</entry>
      <entry>2</entry>
      <entry>3</entry>
      <entry>0</entry>
      <entry>1</entry>
      <entry>2</entry>
      <entry>3</entry>
      <entry>4</entry>
      <entry>5</entry>
      <entry>Handheld</entry>
      <entry>Portable NTSC</entry>
      <entry>Portable PAL</entry>
      <entry>Home Theater NTSC</entry>
      <entry>Home Theater PAL</entry>
      <entry>HDTV</entry>
    </row>
    <row>
      <entry>Width [pixels]</entry>
      <entry>176</entry>
      <entry>176</entry>
      <entry>352</entry>
      <entry>352</entry>
      <entry>176</entry>
      <entry>176</entry>
      <entry>352</entry>
      <entry>352</entry>
      <entry>352</entry>
      <entry>720</entry>
      <entry>176</entry>
      <entry>352</entry>
      <entry>352</entry>
      <entry>720</entry>
      <entry>720</entry>
      <entry>1280</entry>
    </row>
    <row>
      <entry>Height [pixels]</entry>
      <entry>144</entry>
      <entry>144</entry>
      <entry>288</entry>
      <entry>288</entry>
      <entry>144</entry>
      <entry>144</entry>
      <entry>288</entry>
      <entry>288</entry>
      <entry>576</entry>
      <entry>576</entry>
      <entry>144</entry>
      <entry>240</entry>
      <entry>288</entry>
      <entry>480</entry>
      <entry>576</entry>
      <entry>720</entry>
    </row>
    <row>
      <entry>Frame rate [fps]</entry>
      <entry>15</entry>
      <entry>15</entry>
      <entry>15</entry>
      <entry>15</entry>
      <entry>30</entry>
      <entry>30</entry>
      <entry>15</entry>
      <entry>30</entry>
      <entry>30</entry>
      <entry>30</entry>
      <entry>15</entry>
      <entry>30</entry>
      <entry>25</entry>
      <entry>30</entry>
      <entry>25</entry>
      <entry>30</entry>
    </row>
    <row>
      <entry>Max average bitrate [kbps]</entry>
      <entry>64</entry>
      <entry>64</entry>
      <entry>128</entry>
      <entry>384</entry>
      <entry>128</entry>
      <entry>128</entry>
      <entry>384</entry>
      <entry>768</entry>
      <entry>3000</entry>
      <entry>8000</entry>
      <entry>537.6</entry>
      <entry>4854</entry>
      <entry>4854</entry>
      <entry>4854</entry>
      <entry>4854</entry>
      <entry>9708.4</entry>
    </row>
    <row>
      <entry>Peak average bitrate over 3 secs [kbps]</entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry>800</entry>
      <entry>8000</entry>
      <entry>8000</entry>
      <entry>8000</entry>
      <entry>8000</entry>
      <entry>16000</entry>
    </row>
    <row>
      <entry>Max. B-frames</entry>
      <entry>0</entry>
      <entry>0</entry>
      <entry>0</entry>
      <entry>0</entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry>0</entry>
      <entry>1</entry>
      <entry>1</entry>
      <entry>1</entry>
      <entry>1</entry>
      <entry>2</entry>
    </row>
    <row>
      <entry>MPEG quantization</entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry>X</entry>
      <entry>X</entry>
      <entry>X</entry>
      <entry>X</entry>
      <entry>X</entry>
      <entry>X</entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
    </row>
    <row>
      <entry>Adaptive quantization</entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry>X</entry>
      <entry>X</entry>
      <entry>X</entry>
      <entry>X</entry>
      <entry>X</entry>
      <entry>X</entry>
      <entry>X</entry>
      <entry>X</entry>
      <entry>X</entry>
      <entry>X</entry>
      <entry>X</entry>
      <entry>X</entry>
    </row>
    <row>
      <entry>Interlaced encoding</entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry>X</entry>
      <entry>X</entry>
      <entry>X</entry>
      <entry>X</entry>
      <entry>X</entry>
      <entry>X</entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry>X</entry>
      <entry>X</entry>
      <entry>X</entry>
    </row>
    <row>
      <entry>Quaterpixel</entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry>X</entry>
      <entry>X</entry>
      <entry>X</entry>
      <entry>X</entry>
      <entry>X</entry>
      <entry>X</entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
    </row>
    <row>
      <entry>Global motion compensation</entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry>X</entry>
      <entry>X</entry>
      <entry>X</entry>
      <entry>X</entry>
      <entry>X</entry>
      <entry>X</entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
      <entry></entry>
    </row>
  </tbody>
</tgroup>
</informaltable>
</sect2>

<sect2 id="menc-feat-xvid-example-settings">
<title>Encoding setting examples</title>

<para>
  The following settings are examples of different encoding
  option combinations that affect the speed vs quality tradeoff
  at the same target bitrate.
</para>

<para>
  All the encoding settings were tested on a 720x448 @30000/1001 fps
  video sample, the target bitrate was 900kbps, and the machine was an
  AMD-64 3400+ at 2400 Mhz in 64 bits mode.
  Each encoding setting features the measured encoding speed (in
  frames per second) and the PSNR loss (in dB) compared to the "very
  high quality" setting.
  Please understand that depending on your source, your machine type
  and development advancements, you may get very different results.
</para>

<para>
<informaltable frame="all">
<tgroup cols="4">
<thead>
<row><entry>Description</entry><entry>Encoding options</entry><entry>speed (in fps)</entry><entry>Relative PSNR loss (in dB)</entry></row>
</thead>
<tbody>
<row>
  <entry>Very high quality</entry>
  <entry><option>chroma_opt:vhq=4:bvhq=1:quant_type=mpeg</option></entry>
  <entry>16fps</entry>
  <entry>0dB</entry>
</row>
<row>
  <entry>High quality</entry>
  <entry><option>vhq=2:bvhq=1:chroma_opt:quant_type=mpeg</option></entry>
  <entry>18fps</entry>
  <entry>-0.1dB</entry>
</row>
<row>
  <entry>Fast</entry>
  <entry><option>turbo:vhq=0</option></entry>
  <entry>28fps</entry>
  <entry>-0.69dB</entry>
</row>
<row>
  <entry>Realtime</entry>
  <entry><option>turbo:nochroma_me:notrellis:max_bframes=0:vhq=0</option></entry>
  <entry>38fps</entry>
  <entry>-1.48dB</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</para>
</sect2>

</sect1>

<sect1 id="menc-feat-x264">
<title>Encoding with the <systemitem class="library">x264</systemitem> codec</title>
<para>
  <systemitem class="library">x264</systemitem> is a free library for
  encoding H.264/AVC video streams.
  Before starting to encode, you need to <link linkend="codec-x264-encode">
  set up <application>MEncoder</application> to support it</link>.
</para>

<sect2 id="menc-feat-x264-encoding-options">
<title>Encoding options of x264</title>

<para>
  Please begin by reviewing the
  <systemitem class="library">x264</systemitem> section of
  <application>MPlayer</application>'s man page.
  This section is intended to be a supplement to the man page.
  Here you will find quick hints about which options are most
  likely to interest most people. The man page is more terse,
  but also more exhaustive, and it sometimes offers much better
  technical detail.
</para>

<sect3 id="menc-feat-x264-encoding-options-intro">
<title>Introduction</title>
<para>This guide considers two major categories of encoding options:</para>

<orderedlist>
  <listitem><para>Options which mainly trade off encoding time vs. quality
  </para></listitem>
  <listitem><para>Options which may be useful for fulfilling various personal
  preferences and special requirements</para></listitem>
</orderedlist>

<para>
  Ultimately, only you can decide which options are best for your
  purposes. The decision for the first class of options is the simplest:
  you only have to decide whether you think the quality differences
  justify the speed differences. For the second class of options,
  preferences may be far more subjective, and more factors may be
  involved. Note that some of the "personal preferences and special
  requirements" options can still have large impacts on speed or quality,
  but that is not what they are primarily useful for. A couple of the
  "personal preference" options may even cause changes that look better
  to some people, but look worse to others.
</para>

<para>
  Before continuing, you need to understand that this guide uses only one
  quality metric: global PSNR.
  For a brief explanation of what PSNR is, see
  <ulink url="http://en.wikipedia.org/wiki/PSNR">the Wikipedia article on PSNR</ulink>.
  Global PSNR is the last PSNR number reported when you include
  the <option>psnr</option> option in <option>x264encopts</option>.
  Any time you read a claim about PSNR, one of the assumptions
  behind the claim is that equal bitrates are used.
</para>

<para>
  Nearly all of this guide's comments assume you are using
  two pass.
  When comparing options, there are two major reasons for using
  two pass encoding.
  First, using two pass often gains around 1dB PSNR, which is a
  very big difference.
  Secondly, testing options by doing direct quality comparisons
  with one pass encodes introduces a major confounding
  factor: bitrate often varies significantly with each encode.
  It is not always easy to tell whether quality changes are due
  mainly to changed options, or if they mostly reflect essentially
  random differences in the achieved bitrate.
</para>

</sect3>

<sect3 id="menc-feat-x264-encoding-options-speedvquality">
<title>Options which primarily affect speed and quality</title>

<itemizedlist>
<listitem><para>
  <emphasis role="bold">subq</emphasis>:
  Of the options which allow you to trade off speed for quality,
  <option>subq</option> and <option>frameref</option> (see below) are usually
  by far the most important.
  If you are interested in tweaking either speed or quality, these
  are the first options you should consider.
  On the speed dimension, the <option>frameref</option> and
  <option>subq</option> options interact with each other fairly
  strongly.
  Experience shows that, with one reference frame,
  <option>subq=5</option> (the default setting) takes about 35% more time than
  <option>subq=1</option>.
  With 6 reference frames, the penalty grows to over 60%.
  <option>subq</option>'s effect on PSNR seems fairly constant
  regardless of the number of reference frames.
  Typically, <option>subq=5</option> achieves 0.2-0.5 dB higher global
  PSNR in comparison <option>subq=1</option>.
  This is usually enough to be visible.
</para>
<para>
  <option>subq=6</option> is the slowest, highest quality mode.
  In comparison to <option>subq=5</option>, it usually gains 0.1-0.4 dB
  global PSNR with speed costs varying from 25%-100%.
  Unlike other levels of <option>subq</option>, the behavior of
  <option>subq=6</option> does not depend much on <option>frameref</option>
  and <option>me</option>.  Instead, the effectiveness of <option>subq=6
  </option> depends mostly upon the number of B-frames used. In normal
  usage, this means <option>subq=6</option> has a large impact on both speed
  and quality in complex, high motion scenes, but it may not have much effect
  in low-motion scenes. Note that it is still recommended to always set
  <option>bframes</option> to something other than zero (see below).
</para></listitem>
<listitem><para>
  <emphasis role="bold">frameref</emphasis>:
  <option>frameref</option> is set to 1 by default, but this
  should not be taken to imply that it is reasonable to set it
  to 1.
  Merely raising <option>frameref</option> to 2 gains around
  0.15dB PSNR with a 5-10% speed penalty; this seems like a
  good tradeoff.
  <option>frameref=3</option> gains around 0.25dB PSNR over
  <option>frameref=1</option>, which should be a visible
  difference.
  <option>frameref=3</option> is around 15% slower than
  <option>frameref=1</option>.
  Unfortunately, diminishing returns set in rapidly.
  <option>frameref=6</option> can be expected to gain only
  0.05-0.1 dB over <option>frameref=3</option> at an additional
  15% speed penalty.
  Above <option>frameref=6</option>, the quality gains are
  usually very small (although you should keep in mind throughout
  this whole discussion that it can vary quite a lot depending on
  your source).
  In a fairly typical case, <option>frameref=12</option>
  will improve global PSNR by a tiny 0.02dB over
  <option>frameref=6</option>, at a speed cost of 15%-20%.
  At such high <option>frameref</option> values, the only really
  good thing that can be said is that increasing it even further will
  almost certainly never <emphasis role="bold">harm</emphasis>
  PSNR, but the additional quality benefits are barely even
  measurable, let alone perceptible.
</para>
<note><title>Note:</title>
<para>
  Raising <option>frameref</option> to unnecessarily high values
  <emphasis role="bold">can</emphasis> and
  <emphasis role="bold">usually does</emphasis>
  hurt coding efficiency if you turn CABAC off.
  With CABAC on (the default behavior), the possibility of setting
  <option>frameref</option> "too high" currently seems too remote
  to even worry about, and in the future, optimizations may remove
  the possibility altogether.
</para>
</note>
<para>
  If you care about speed, a reasonable compromise is to use low
  <option>subq</option> and <option>frameref</option> values on
  the first pass, and then raise them on the second pass.
  Typically, this has a negligible negative effect on the final
  quality: You will probably lose well under 0.1dB PSNR, which
  should be much too small of a difference to see.
  However, different values of <option>frameref</option> can
  occasionally affect frametype decision.
  Most likely, these are rare outlying cases, but if you want to
  be pretty sure, consider whether your video has either
  fullscreen repetitive flashing patterns or very large temporary
  occlusions which might force an I-frame.
  Adjust the first-pass <option>frameref</option> so it is large
  enough to contain the duration of the flashing cycle (or occlusion).
  For example, if the scene flashes back and forth between two images
  over a duration of three frames, set the first pass
  <option>frameref</option> to 3 or higher.
  This issue is probably extremely rare in live action video material,
  but it does sometimes come up in video game captures.
</para></listitem>

<listitem><para>
  <emphasis role="bold">me</emphasis>:
  This option is for choosing the motion estimation search method.
  Altering this option provides a straightforward quality-vs-speed
  tradeoff. <option>me=1</option> is only a few percent faster than
  the default search, at a cost of under 0.1dB global PSNR. The 
  default setting (<option>me=2</option>) is a reasonable tradeoff
  between speed and quality. <option>me=3</option> gains a little under
  0.1dB global PSNR, with a speed penalty that varies depending on
  <option>frameref</option>.  At high values of
  <option>frameref</option> (e.g. 12 or so), <option>me=3</option>
  is about 40% slower than the default <option> me=2</option>. With
  <option>frameref=3</option>, the speed penalty incurred drops to
  25%-30%.
</para>
<para>
  <option>me=4</option> uses an exhaustive search that is too slow for
  practical use.
</para>
</listitem>

<listitem><para>
  <emphasis role="bold">4x4mv</emphasis>:
  This option enables the use of 8x4, 4x8 and 4x4 subpartitions in
  predicted macroblocks. Enabling it results in a fairly consistent
  10%-15% loss of speed. This option is rather useless in source
  containing only low motion, however in some high-motion source,
  particularly source with lots of small moving objects, gains of
  about 0.1dB can be expected.
</para>
</listitem>

<listitem><para>
  <emphasis role="bold">bframes</emphasis>:
  If you are used to encoding with other codecs, you may have found
  that B-frames are not always useful.
  In H.264, this has changed: there are new techniques and block
  types that are possible in B-frames.
  Usually, even a naive B-frame choice algorithm can have a
  significant PSNR benefit.
  It is interesting to note that using B-frames usually speeds up
  the second pass somewhat, and may also speed up a single
  pass encode if adaptive B-frame decision is turned off.
</para>
<para>
  With adaptive B-frame decision turned off
  (<option>x264encopts</option>'s <option>nob_adapt</option>),
  the optimal value for this setting is usually no more than
  <option>bframes=1</option>, or else high-motion scenes can suffer.
  With adaptive B-frame decision on (the default behavior), it is
  safe to use higher values; the encoder will reduce the use of
  B-frames in scenes where they would hurt compression.
  The encoder rarely chooses to use more than 3 or 4 B-frames;
  setting this option any higher will have little effect.
</para></listitem>

<listitem><para>
  <emphasis role="bold">b_adapt</emphasis>:
  Note: This is on by default.
</para>
<para>
  With this option enabled, the encoder will use a reasonably fast
  decision process to reduce the number of B-frames used in scenes that
  might not benefit from them as much.
  You can use <option>b_bias</option> to tweak how B-frame-happy
  the encoder is.
  The speed penalty of adaptive B-frames is currently rather modest,
  but so is the potential quality gain.
  It usually does not hurt, however.
  Note that this only affects speed and frametype decision on the
  first pass.
  <option>b_adapt</option> and <option>b_bias</option> have no
  effect on subsequent passes.
</para></listitem>

<listitem><para>
  <emphasis role="bold">b_pyramid</emphasis>:
  You might as well enable this option if you are using >=2 B-frames;
  as the man page says, you get a little quality improvement at no
  speed cost.
  Note that these videos cannot be read by libavcodec-based decoders
  older than about March 5, 2005.
</para></listitem>

<listitem><para>
  <emphasis role="bold">weight_b</emphasis>:
  In typical cases, there is not much gain with this option.
  However, in crossfades or fade-to-black scenes, weighted
  prediction gives rather large bitrate savings.
  In MPEG-4 ASP, a fade-to-black is usually best coded as a series
  of expensive I-frames; using weighted prediction in B-frames
  makes it possible to turn at least some of these into much smaller
  B-frames.
  Encoding time cost is minimal, as no extra decisions need to be made.
  Also, contrary to what some people seem to guess, the decoder
  CPU requirements are not much affected by weighted prediction,
  all else being equal.
</para>
<para>
  Unfortunately, the current adaptive B-frame decision algorithm
  has a strong tendency to avoid B-frames during fades.
  Until this changes, it may be a good idea to add
  <option>nob_adapt</option> to your x264encopts, if you expect
  fades to have a large effect in your particular video
  clip.
</para></listitem>
</itemizedlist>
</sect3>

<sect3 id="menc-feat-x264-encoding-options-misc-preferences">
<title>Options pertaining to miscellaneous preferences</title>
<itemizedlist>
<listitem><para>
  <emphasis role="bold">Two pass encoding</emphasis>:
  Above, it was suggested to always use two pass encoding, but there
  are still reasons for not using it. For instance, if you are capturing
  live TV and encoding in realtime, you are forced to use single-pass.
  Also, one pass is obviously faster than two passes; if you use the
  exact same set of options on both passes, two pass encoding is almost
  twice as slow.
</para>
<para>
  Still, there are very good reasons for using two pass encoding. For
  one thing, single pass ratecontrol is not psychic, and it often makes
  unreasonable choices because it cannot see the big picture. For example,
  suppose you have a two minute long video consisting of two distinct
  halves.  The first half is a very high-motion scene lasting 60 seconds
  which, in isolation, requires about 2500kbps in order to look decent.
  Immediately following it is a much less demanding 60-second scene
  that looks good at 300kbps. Suppose you ask for 1400kbps on the theory
  that this is enough to accomodate both scenes. Single pass ratecontrol
  will make a couple of "mistakes" in such a case. First of all, it
  will target 1400kbps in both segments. The first segment may end up
  heavily overquantized, causing it to look unacceptably and unreasonably
  blocky. The second segment will be heavily underquantized; it may look
  perfect, but the bitrate cost of that perfection will be completely
  unreasonable. What is even harder to avoid is the problem at the
  transition between the two scenes. The first seconds of the low motion
  half will be hugely over-quantized, because the ratecontrol is still
  expecting the kind of bitrate requirements it met in the first half
  of the video. This "error period" of heavily over-quantized low motion
  will look jarringly bad, and will actually use less than the 300kbps
  it would have taken to make it look decent. There are ways to
  mitigate the pitfalls of single-pass encoding, but they may tend to
  increase bitrate misprediction.
</para>
<para>
  Multipass ratecontrol can offer huge advantages over a single pass.
  Using the statistics gathered from the first pass encode, the encoder
  can estimate, with reasonable accuracy, the "cost" (in bits) of
  encoding any given frame, at any given quantizer. This allows for
  a much more rational, better planned allocation of bits between the
  expensive (high-motion) and cheap (low-motion) scenes. See
  <option>qcomp</option> below for some ideas on how to tweak this
  allocation to your liking.
</para>
<para>
  Moreover, two passes need not take twice as long as one pass. You can
  tweak the options in the first pass for higher speed and lower quality.
  If you choose your options well, you can get a very fast first pass.
  The resulting quality in the second pass will be slightly lower because size
  prediction is less accurate, but the quality difference is normally much
  too small to be visible. Try, for example, adding
  <option>subq=1:frameref=1</option> to the first pass
  <option>x264encopts</option>. Then, on the second pass, use slower,
  higher-quality options:
  <option>subq=6:frameref=15:4x4mv:me=3</option>
</para></listitem>
<listitem><para>
  <emphasis role="bold">Three pass encoding</emphasis>?

  x264 offers the ability to make an arbitrary number of consecutive
  passes. If you specify <option>pass=1</option> on the first pass,
  then use <option>pass=3</option> on a subsequent pass, the subsequent
  pass will both read the statistics from the previous pass, and write
  its own statistics. An additional pass following this one will have
  a very good base from which to make highly accurate predictions of
  framesizes at a chosen quantizer. In practice, the overall quality
  gain from this is usually close to zero, and quite possibly a third
  pass will result in slightly worse global PSNR than the pass before
  it. In typical usage, three passes help if you get either bad bitrate
  prediction or bad looking scene transitions when using only two passes.
  This is somewhat likely to happen on extremely short clips. There are
  also a few special cases in which three (or more) passes are handy
  for advanced users, but for brevity, this guide omits discussing those
  special cases.

</para></listitem>
<listitem><para>
  <emphasis role="bold">qcomp</emphasis>:
  <option>qcomp</option> trades off the number of bits allocated
  to "expensive" high-motion versus "cheap" low-motion frames. At
  one extreme, <option>qcomp=0</option> aims for true constant
  bitrate. Typically this would make high-motion scenes look completely
  awful, while low-motion scenes would probably look absolutely
  perfect, but would also use many times more bitrate than they
  would need in order to look merely excellent. At the other extreme,
  <option>qcomp=1</option> achieves nearly constant quantization parameter
  (QP). Constant QP does not look bad, but most people think it is more
  reasonable to shave some bitrate off of the extremely expensive scenes
  (where the loss of quality is not as noticeable) and reallocate it to
  the scenes that are easier to encode at excellent quality.
  <option>qcomp</option> is set to 0.6 by default, which may be slightly
  low for many peoples' taste (0.7-0.8 are also commonly used).
</para></listitem>
<listitem><para>
  <emphasis role="bold">keyint</emphasis>:
  <option>keyint</option> is solely for trading off file seekability against
  coding efficiency. By default, <option>keyint</option> is set to 250. In
  25fps material, this guarantees the ability to seek to within 10 seconds
  precision. If you think it would be important and useful to be able to
  seek within 5 seconds of precision, set <option>keyint=125</option>;
  this will hurt quality/bitrate slightly. If you care only about quality
  and not about seekability, you can set it to much higher values
  (understanding that there are diminishing returns which may become
  vanishingly low, or even zero). The video stream will still have seekable
  points as long as there are some scene changes.
</para></listitem> 
<listitem><para>
  <emphasis role="bold">deblockalpha, deblockbeta</emphasis>:
  This topic is going to be a bit controversial.
</para>
<para>
  H.264 defines a simple deblocking procedure on I-blocks that uses
  pre-set strengths and thresholds depending on the QP of the block
  in question.
  By default, high QP blocks are filtered heavily, and low QP blocks
  are not deblocked at all.
  The pre-set strengths defined by the standard are well-chosen and
  the odds are very good that they are PSNR-optimal for whatever
  video you are trying to encode.
  The <option>deblockalpha</option> and <option>deblockbeta</option>
  parameters allow you to specify offsets to the preset deblocking
  thresholds.
</para>
<para>
  Many people seem to think it is a good idea to lower the deblocking
  filter strength by large amounts (say, -3).
  This is however almost never a good idea, and in most cases,
  people who are doing this do not understand very well how
  deblocking works by default.
</para>
<para>
  The first and most important thing to know about the in-loop
  deblocking filter is that the default thresholds are almost always
  PSNR-optimal.
  In the rare cases that they are not optimal, the ideal offset is
  plus or minus 1.
  Adjusting deblocking parameters by a larger amount is almost
  guaranteed to hurt PSNR.
  Strengthening the filter will smear more details; weakening the
  filter will increase the appearance of blockiness.
</para>
<para>
  It is definitely a bad idea to lower the deblocking thresholds if
  your source is mainly low in spacial complexity (i.e., not a lot
  of detail or noise).
  The in-loop filter does a rather excellent job of concealing
  the artifacts that occur.
  If the source is high in spacial complexity, however, artifacts
  are less noticeable.
  This is because the ringing tends to look like detail or noise.
  Human visual perception easily notices when detail is removed,
  but it does not so easily notice when the noise is wrongly
  represented.
  When it comes to subjective quality, noise and detail are somewhat
  interchangeable.
  By lowering the deblocking filter strength, you are most likely
  increasing error by adding ringing artifacts, but the eye does
  not notice because it confuses the artifacts with detail.
</para>

<para>
  This <emphasis role="bold">still</emphasis> does not justify
  lowering the deblocking filter strength, however.
  You can generally get better quality noise from postprocessing.
  If your H.264 encodes look too blurry or smeared, try playing with
  <option>-vf noise</option> when you play your encoded movie.
  <option>-vf noise=8a:4a</option> should conceal most mild
  artifacting.
  It will almost certainly look better than the results you
  would have gotten just by fiddling with the deblocking filter.
</para></listitem>
</itemizedlist>
</sect3>
</sect2>

<sect2 id="menc-feat-x264-example-settings">
<title>Encoding setting examples</title>

<para>
  The following settings are examples of different encoding
  option combinations that affect the speed vs quality tradeoff
  at the same target bitrate.
</para>

<para>
  All the encoding settings were tested on a 720x448 @30000/1001 fps
  video sample, the target bitrate was 900kbps, and the machine was an
  AMD-64 3400+ at 2400 Mhz in 64 bits mode.
  Each encoding setting features the measured encoding speed (in
  frames per second) and the PSNR loss (in dB) compared to the "very
  high quality" setting.
  Please understand that depending on your source, your machine type
  and development advancements, you may get very different results.
</para>

<para>
<informaltable frame="all">
<tgroup cols="4">
<thead>
<row><entry>Description</entry><entry>Encoding options</entry><entry>speed (in fps)</entry><entry>Relative PSNR loss (in dB)</entry></row>
</thead>
<tbody>
<row>
  <entry>Very high quality</entry>
  <entry><option>subq=6:4x4mv:8x8dct:me=3:frameref=5:bframes=3:b_pyramid:weight_b</option></entry>
  <entry>6fps</entry>
  <entry>0dB</entry>
</row>
<row>
  <entry>High quality</entry>
  <entry><option>subq=5:4x4mv:8x8dct:frameref=2:bframes=3:b_pyramid:weight_b</option></entry>
  <entry>13fps</entry>
  <entry>-0.89dB</entry>
</row>
<row>
  <entry>Fast</entry>
  <entry><option>subq=4:bframes=2:b_pyramid:weight_b</option></entry>
  <entry>17fps</entry>
  <entry>-1.48dB</entry>
</row>
</tbody>
</tgroup>
</informaltable>
</para>
</sect2>

</sect1>

<sect1 id="menc-feat-vcd-dvd">
<title>Using MEncoder to create VCD/SVCD/DVD-compliant files.</title>

<sect2 id="menc-feat-vcd-dvd-constraints">
<title>Format Constraints</title>
<para>
  <application>MEncoder</application> is capable of creating VCD, SCVD
  and DVD format MPEG files using the
  <systemitem class="library">libavcodec</systemitem> library.
  These files can then be used in conjunction with
  <ulink url="http://www.gnu.org/software/vcdimager/vcdimager.html">vcdimager</ulink>
  or
  <ulink url="http://dvdauthor.sourceforge.net/">dvdauthor</ulink>
  to create discs that will play on a standard set-top player.
</para>

<para>
  The DVD, SVCD, and VCD formats are subject to heavy constraints.
  Only a small selection of encoded picture sizes and aspect ratios are
  available.
  If your movie does not already meet these requirements, you may have
  to scale,crop or add black borders to the picture to make it
  compliant.
</para>

<sect3 id="menc-feat-vcd-dvd-constraints-resolution">
<title>Format Constraints</title>

<informaltable frame="all">
<tgroup cols="9">
<thead>
    <row>
        <entry>Format</entry>
        <entry>Resolution</entry>
        <entry>V. Codec</entry>
        <entry>V. Bitrate</entry>
        <entry>Sample Rate</entry>
        <entry>A. Codec</entry>
        <entry>A. Bitrate</entry>
        <entry>FPS</entry>
        <entry>Aspect</entry>
    </row>
</thead>
<tbody>
    <row>
        <entry>NTSC DVD</entry>
        <entry>720x480, 704x480, 352x480, 352x240</entry> 
        <entry>MPEG-2</entry>
        <entry>9800 kbps</entry>
        <entry>48000 Hz</entry>
        <entry>AC3,PCM</entry>
        <entry>1536 kbps (max)</entry>
        <entry>30000/1001, 24000/1001</entry>
        <entry>4:3, 16:9 (only for 720x480)</entry>
    </row>
    <row>
        <entry>NTSC DVD</entry>
        <entry>352x240<footnote id='fn-rare-resolutions'><para>
	  These resolutions are rarely used for DVDs because
	  they are fairly low quality.</para></footnote></entry> 
        <entry>MPEG-1</entry>
        <entry>1856 kbps</entry>
        <entry>48000 Hz</entry>
        <entry>AC3,PCM</entry>
        <entry>1536 kbps (max)</entry>
        <entry>30000/1001, 24000/1001</entry>
        <entry>4:3, 16:9</entry>
    </row>
    <row>
        <entry>NTSC SVCD</entry>
        <entry>480x480</entry>
        <entry>MPEG-2</entry>
        <entry>2600 kbps</entry>
        <entry>44100 Hz</entry>
        <entry>MP2</entry>
        <entry>384 kbps (max)</entry>
        <entry>30000/1001</entry>
        <entry>4:3</entry>
    </row>
    <row>
        <entry>NTSC VCD</entry>
        <entry>352x240</entry>
        <entry>MPEG-1</entry>
        <entry>1150 kbps</entry>
        <entry>44100 Hz</entry>
        <entry>MP2</entry>
        <entry>224 kbps</entry>
        <entry>24000/1001, 30000/1001</entry>
        <entry>4:3</entry>
    </row>
    <row>
        <entry>PAL DVD</entry>
        <entry>720x576, 704x576, 352x576, 352x288</entry>
        <entry>MPEG-2</entry>
        <entry>9800 kbps</entry>
        <entry>48000 Hz</entry>
        <entry>MP2,AC3,PCM</entry>
        <entry>1536 kbps (max)</entry>
        <entry>25</entry>
        <entry>4:3, 16:9 (only for 720x576)</entry>
    </row>
    <row>
        <entry>PAL DVD</entry>
        <entry>352x288<footnoteref linkend='fn-rare-resolutions'/></entry>
        <entry>MPEG-1</entry>
        <entry>1856 kbps</entry>
        <entry>48000 Hz</entry>
        <entry>MP2,AC3,PCM</entry>
        <entry>1536 kbps (max)</entry>
        <entry>25</entry>
        <entry>4:3, 16:9</entry>
    </row>
    <row>
        <entry>PAL SVCD</entry>
        <entry>480x576</entry>
        <entry>MPEG-2</entry>
        <entry>2600 kbps</entry>
        <entry>44100 Hz</entry>
        <entry>MP2</entry>
        <entry>384 kbps (max)</entry>
        <entry>25</entry>
        <entry>4:3</entry>
    </row>
    <row>
        <entry>PAL VCD</entry>
        <entry>352x288</entry>
        <entry>MPEG-1</entry>
        <entry>1152 kbps</entry>
        <entry>44100 Hz</entry>
        <entry>MP2</entry>
        <entry>224 kbps</entry>
        <entry>25</entry>
        <entry>4:3</entry>
    </row>
</tbody>
</tgroup>
</informaltable>

<para>
  If your movie has 2.35:1 aspect (most recent action movies), you will
  have to add black borders or crop the movie down to 16:9 to make a DVD
  or VCD.
  If you add black borders, try to align them at 16-pixel boundaries in
  order to minimize the impact on encoding performance.
  Thankfully DVD has sufficiently excessive bitrate that you do not have
  to worry too much about encoding efficiency, but SVCD and VCD are
  highly bitrate-starved and require effort to obtain acceptable quality.
</para>
</sect3>

<sect3 id="menc-feat-vcd-dvd-constraints-gop">
<title>GOP Size Constraints</title>
<para>
  DVD, VCD, and SVCD also constrain you to relatively low 
  GOP (Group of Pictures) sizes.
  For 30 fps material the largest allowed GOP size is 18.
  For 25 or 24 fps, the maximum is 15.
  The GOP size is set using the <option>keyint</option> option.
</para>
</sect3>

<sect3 id="menc-feat-vcd-dvd-constraints-bitrate">
<title>Bitrate Constraints</title>
<para>
  VCD video is required to be CBR at 1152 kbps.
  This highly limiting constraint also comes along with an extremly low vbv
  buffer size of 327 kilobits.
  SVCD allows varying video bitrates up to 2500 kbps, and a somewhat less 
  restrictive vbv buffer size of 917 kilobits is allowed.
  DVD video bitrates may range anywhere up to 9800 kbps (though typical
  bitrates are about half that), and the vbv buffer size is 1835 kilobits.
</para>
</sect3>
</sect2>

<sect2 id="menc-feat-vcd-dvd-output">
<title>Output Options</title>
<para>
  <application>MEncoder</application> has options to control the output
  format.
  Using these options we can instruct it to create the correct type of
  file.
</para>

<para>
  The options for VCD and SVCD are called xvcd and xsvcd, because they
  are extended formats.
  They are not strictly compliant, mainly because the output does not
  contain scan offsets.
  If you need to generate an SVCD image, you  should pass the output file
  to
  <ulink url="http://www.gnu.org/software/vcdimager/vcdimager.html">vcdimager</ulink>.
</para>

<para>
  VCD:
  <screen>
  -of mpeg -mpegopts format=xvcd
  </screen>
</para>

<para>
  SVCD:
  <screen>
  -of mpeg -mpegopts format=xsvcd
  </screen>
</para>

<para>
  DVD:
  <screen>
  -of mpeg -mpegopts format=dvd
  </screen>
</para>

<para>
  DVD with NTSC Pullup:
  <screen>
  -of mpeg -mpegopts format=dvd:telecine -ofps 24000/1001
  </screen>
  This allows 24000/1001 fps progressive content to be encoded at 30000/1001 
  fps whilst maintaing DVD-compliance.
</para>

<sect3 id="menc-feat-vcd-dvd-output-aspect">
<title>Aspect Ratio</title>
<para>
  The aspect argument of <option>-lavcopts</option> is used to encode
  the aspect ratio of the file.
  During playback the aspect ratio is used to restore the video to the
  correct size.
</para>

<para>
  16:9 or "Widescreen"
  <screen>
  -lavcopts aspect=16/9
  </screen>
</para>

<para>
  4:3 or "Fullscreen"
  <screen>
  -lavcopts aspect=4/3
  </screen>
</para>

<para>
  2.35:1 or "Cinemascope" NTSC
  <screen>
  -vf scale=720:368,expand=720:480 -lavcopts aspect=16/9
  </screen>
  To calculate the correct scaling size, use the expanded NTSC width of
  854/2.35 = 368
</para>

<para>
  2.35:1 or "Cinemascope" PAL
  <screen>
  -vf scale="720:432,expand=720:576 -lavcopts aspect=16/9
  </screen>
  To calculate the correct scaling size, use the expanded PAL width of
  1024/2.35 = 432
</para>

</sect3>

<sect3 id="menc-feat-vcd-dvd-output-srate">
<title>Sample Rate Conversion</title>
<para>
  If the audio sample rate in the original file is not the same as
  required by the target format, sample rate conversion is required.
  This is achieved using the <option>-srate</option> option and 
  the <option>-af lavcresample</option> audio filter together.
  </para>
  <para>
  DVD:
  <screen>
  -srate 48000 -af lavcresample=48000
  </screen>
</para>
<para>
  VCD and SVCD:
  <screen>
  -srate 44100 -af lavcresample=44100
  </screen>
  </para>
</sect3>
</sect2>

<sect2 id="menc-feat-vcd-dvd-lavc">
<title>Using libavcodec for VCD/SVCD/DVD Encoding</title>

<sect3 id="menc-feat-vcd-dvd-lavc-intro">
<title>Introduction</title>
<para>
  <systemitem class="library">libavcodec</systemitem> can be used to
  create VCD/SVCD/DVD compliant video by using the appropriate options.
</para>
</sect3>

<sect3 id="menc-feat-vcd-dvd-lavc-options">
<title>lavcopts</title>
<para>
  This is a list of fields in <option>-lavcopts</option> that you may
  be required to change in order to make a complaint movie for VCD, SVCD,
  or DVD:
</para>

<itemizedlist>
<listitem><para>
  <emphasis role="bold">acodec</emphasis>:
  <option>mp2</option> for VCD, SVCD, or PAL DVD;
  <option>ac3</option> is most commonly used for DVD.
  PCM audio may also be used for DVD, but this is mostly a big waste of
  space.
  Note that MP3 audio is not compliant for any of these formats, but
  players often have no problem playing it anyway.
</para></listitem>

<listitem><para>
  <emphasis role="bold">abitrate</emphasis>:
  224 for VCD; up to 384 for SVCD; up to 1536 for  DVD, but commonly
  used values range from 192 kbps for stereo to 384 kbps for 5.1 channel
  sound.
</para></listitem>

<listitem><para>
  <emphasis role="bold">vcodec</emphasis>:
  <option>mpeg1video</option> for VCD;
  <option>mpeg2video</option> for SVCD;
  <option>mpeg2video</option> is usually used for DVD but you may also use
  <option>mpeg1video</option> for CIF resolutions.
</para></listitem>

<listitem><para>
  <emphasis role="bold">keyint</emphasis>:
  Used to set the GOP size.
  18 for 30fps material, or 15 for 25/24 fps material.
  Commercial producers seem to prefer keyframe intervals of 12.
  It is possible to make this much larger and still retain compatibility 
  with most players.
  A <option>keyint</option> of 25 should never cause any problems.
</para></listitem>

<listitem><para>
  <emphasis role="bold">vrc_buf_size</emphasis>:
  327 for VCD, 917 for SVCD, and 1835 for DVD.
</para></listitem>

<listitem><para>
  <emphasis role="bold">vrc_minrate</emphasis>:
  1152, for VCD. May be left alone for SVCD and DVD.
</para></listitem>

<listitem><para>
  <emphasis role="bold">vrc_maxrate</emphasis>:
  1152 for VCD; 2500 for SVCD; 9800 for DVD.
  For SVCD and DVD, you might wish to use lower values depending on your
  own personal preferences and requirements.
</para></listitem>

<listitem><para>
  <emphasis role="bold">vbitrate</emphasis>:
  1152 for VCD;
  up to 2500 for SVCD;
  up to 9800 for DVD.
  For the latter two formats, vbitrate should be set based on personal
  preference.
  For instance, if you insist on fitting 20 or so hours on a DVD, you
  could use vbitrate=400.
  The resulting video quality would probably be quite bad.
  If you are trying to squeeze out the maximum possible quality on a DVD,
  use vbitrate=9800, but be warned that this could constrain you to less
  than an hour of video on a single-layer DVD.
</para></listitem>
</itemizedlist>
</sect3>

<sect3 id="menc-feat-vcd-dvd-lavc-examples">
<title>Examples</title>
<para>
  This is a typical minimum set of <option>-lavcopts</option> for
  encoding video:
</para>
<para>
  VCD:
  <screen>
  -lavcopts vcodec=mpeg1video:vrc_buf_size=327:vrc_minrate=1152:\
  vrc_maxrate=1152:vbitrate=1152:keyint=15:acodec=mp2
  </screen>
</para>

<para>
  SVCD:
  <screen>
  -lavcopts vcodec=mpeg2video:vrc_buf_size=917:vrc_maxrate=2500:vbitrate=1800:\
  keyint=15:acodec=mp2
  </screen>
</para>

<para>
  DVD:
  <screen>
  -lavcopts vcodec=mpeg2video:vrc_buf_size=1835:vrc_maxrate=9800:vbitrate=5000:\
  keyint=15:acodec=ac3
  </screen>
</para>

</sect3>

<sect3 id="menc-feat-vcd-dvd-lavc-advanced">
<title>Advanced Options</title>
<para>
  For higher quality encoding, you may also wish to add quality-enhancing
  options to lavcopts, such as <option>trell</option>,
  <option>mbd=2</option>, and others.
  Note that <option>qpel</option> and <option>v4mv</option>, while often
  useful with MPEG-4, are not usable with MPEG-1 or MPEG-2.
  Also, if you are trying to make a very high quality DVD encode, it may
  be useful to add <option>dc=10</option> to lavcopts.
  Doing so may help reduce the appearance of blocks in flat-colored areas.
  Putting it all together, this is an example of a set of lavcopts for a
  higher quality DVD:
</para>

<para>
  <screen>
  -lavcopts vcodec=mpeg2video:vrc_buf_size=1835:vrc_maxrate=9800:vbitrate=8000:\
  keyint=15:trell:mbd=2:precmp=2:subcmp=2:cmp=2:dia=-10:predia=-10:cbp:mv0:\
  vqmin=1:lmin=1:dc=10
  </screen>
</para>

</sect3>
</sect2>

<sect2 id="menc-feat-vcd-dvd-audio">
<title>Encoding Audio</title>
<para>
  VCD and SVCD support MPEG-1 layer II audio, using one of
  <systemitem class="library">toolame</systemitem>,
  <systemitem class="library">twolame</systemitem>,
  or <systemitem class="library">libavcodec</systemitem>'s MP2 encoder.
  The libavcodec MP2 is far from being as good as the other two libraries,
  however it should always be available to use.
  VCD only supports constant bitrate audio (CBR) whereas SVCD supports
  variable bitrate (VBR), too.
  Be careful when using VBR because some bad standalone players might not
  support it too well.
</para>

<para>
  For DVD audio, <systemitem class="library">libavcodec</systemitem>'s
  AC3 codec is used.
</para>

<sect3 id="menc-feat-vcd-dvd-audio-toolame">
<title>toolame</title>
<para>
  For VCD and SVCD:
  <screen>
  -oac toolame -toolameopts br=224
  </screen>
</para>
</sect3>

<sect3 id="menc-feat-vcd-dvd-audio-twolame">
<title>twolame</title>
<para>
  For VCD and SVCD:
  <screen>
  -oac twolame -twolameopts br=224
  </screen>
</para>
</sect3>

<sect3 id="menc-feat-vcd-dvd-audio-lavc">
<title>libavcodec</title>
<para>
  For DVD with 2 channel sound:
  <screen>
  -oac lavc -lavcopts acodec=ac3:abitrate=192
  </screen>
</para>
<para>
  For DVD with 5.1 channel sound:
  <screen>
  -channels 6 -oac lavc -lavcopts acodec=ac3:abitrate=384
  </screen>
</para>
<para>
  For VCD and SVCD:
  <screen>
  -oac lavc -lavcopts acodec=mp2:abitrate=224
  </screen>
</para>
</sect3>

</sect2>

<sect2 id="menc-feat-vcd-dvd-all">
<title>Putting it all Together</title>
<para>
  This section shows some complete commands for creating VCD/SVCD/DVD
  compliant videos.
</para>

<sect3 id="menc-feat-vcd-dvd-all-pal-dvd">
<title>PAL DVD</title>
<para>
  <screen>
  mencoder -oac lavc -ovc lavc -of mpeg -mpegopts format=dvd -vf scale=720:576,\
  harddup -srate 48000 -af lavcresample=48000 -lavcopts vcodec=mpeg2video:\
  vrc_buf_size=1835:vrc_maxrate=9800:vbitrate=5000:keyint=15:acodec=ac3:\
  abitrate=192:aspect=16/9 -ofps 25 \
  -o <replaceable>movie.mpg</replaceable> <replaceable>movie.avi</replaceable>
  </screen>
</para>
</sect3>

<sect3 id="menc-feat-vcd-dvd-all-ntsc-dvd">
<title>NTSC DVD</title>
<para>
  <screen>
  mencoder -oac lavc -ovc lavc -of mpeg -mpegopts format=dvd -vf scale=720:480,\
  harddup -srate 48000 -af lavcresample=48000 -lavcopts vcodec=mpeg2video:\
  vrc_buf_size=1835:vrc_maxrate=9800:vbitrate=5000:keyint=18:acodec=ac3:\
  abitrate=192:aspect=16/9 -ofps 30000/1001 \
  -o <replaceable>movie.mpg</replaceable> <replaceable>movie.avi</replaceable>
  </screen>
</para>
</sect3>

<sect3 id="menc-feat-vcd-dvd-all-pal-ac3-copy">
<title>PAL AVI Containing AC3 Audio to DVD</title>
<para>
  If the source already has AC3 audio, use -oac copy instead of re-encoding it.
  <screen>
  mencoder -oac copy -ovc lavc -of mpeg -mpegopts format=dvd -vf scale=720:576,\
  harddup -lavcopts vcodec=mpeg2video:vrc_buf_size=1835:vrc_maxrate=9800:\
  vbitrate=5000:keyint=15:aspect=16/9 -ofps 25 \
  -o <replaceable>movie.mpg</replaceable> <replaceable>movie.avi</replaceable>
  </screen>
</para>
</sect3>

<sect3 id="menc-feat-vcd-dvd-all-ntsc-ac3-copy">
<title>NTSC AVI Containing AC3 Audio to DVD</title>
<para>
  If the source already has AC3 audio, and is NTSC @ 24000/1001 fps:
  <screen>
  mencoder -oac copy -ovc lavc -of mpeg -mpegopts format=dvd:telecine \
  -vf scale=720:480,harddup -lavcopts vcodec=mpeg2video:vrc_buf_size=1835:\
  vrc_maxrate=9800:vbitrate=5000:keyint=15:aspect=16/9 -ofps 24000/1001 \
  -o <replaceable>movie.mpg</replaceable> <replaceable>movie.avi</replaceable>
  </screen>
</para>
</sect3>

<sect3 id="menc-feat-vcd-dvd-all-pal-svcd">
<title>PAL SVCD</title>
<para>
  <screen>
  mencoder -oac lavc -ovc lavc -of mpeg -mpegopts format=xsvcd -vf \
  scale=480:576,harddup -srate 44100 -af lavcresample=44100 -lavcopts \
  vcodec=mpeg2video:mbd=2:keyint=15:vrc_buf_size=917:vrc_minrate=600:\
  vbitrate=2500:vrc_maxrate=2500:acodec=mp2:abitrate=224 -ofps 25 \
  -o <replaceable>movie.mpg</replaceable> <replaceable>movie.avi</replaceable>
  </screen>
</para>
</sect3>

<sect3 id="menc-feat-vcd-dvd-all-ntsc-svcd">
<title>NTSC SVCD</title>
<para>
  <screen>
  mencoder -oac lavc -ovc lavc -of mpeg -mpegopts format=xsvcd  -vf \
  scale=480:480,harddup -srate 44100 -af lavcresample=44100 -lavcopts \
  vcodec=mpeg2video:mbd=2:keyint=18:vrc_buf_size=917:vrc_minrate=600:\
  vbitrate=2500:vrc_maxrate=2500:acodec=mp2:abitrate=224 -ofps 30000/1001 \
  -o <replaceable>movie.mpg</replaceable> <replaceable>movie.avi</replaceable>
  </screen>
</para>
</sect3>

<sect3 id="menc-feat-vcd-dvd-all-pal-vcd">
<title>PAL VCD</title>
<para>
  <screen>
  mencoder -oac lavc -ovc lavc -of mpeg -mpegopts format=xvcd -vf \
  scale=352:288,harddup -srate 44100 -af lavcresample=44100 -lavcopts \
  vcodec=mpeg1video:keyint=15:vrc_buf_size=327:vrc_minrate=1152:vbitrate=1152:\
  vrc_maxrate=1152:acodec=mp2:abitrate=224 -ofps 25 \
  -o <replaceable>movie.mpg</replaceable> <replaceable>movie.avi</replaceable>
  </screen>
</para>
</sect3>

<sect3 id="menc-feat-vcd-dvd-all-ntsc-vcd">
<title>NTSC VCD</title>
<para>
  <screen>
  mencoder -oac lavc -ovc lavc -of mpeg -mpegopts format=xvcd -vf \
  scale=352:240,harddup -srate 44100 -af lavcresample=44100 -lavcopts \
  vcodec=mpeg1video:keyint=18:vrc_buf_size=327:vrc_minrate=1152:vbitrate=1152:\
  vrc_maxrate=1152:acodec=mp2:abitrate=224 -ofps 30000/1001 \
  -o <replaceable>movie.mpg</replaceable> <replaceable>movie.avi</replaceable>
  </screen>
</para>
</sect3>

</sect2>

</sect1>

</chapter>
