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====== Transcode ======

===== Conversione di un DivX danneggiato in XviD =====

Procedura utilizzata per correggere un file DivX danneggiato. Avidemux non era in grado di aprire il file.

Per cominciare con mplayer (che pare essere più bravo a decodificare file danneggiati) si è convertito in //yuv4mpeg// (vedere l'opzione ''**-vo yuv4mpeg**'').

Con ''**transcode**'' si converte un file dal formato //yuv4mpeg// al formato //XviD//. Prima bisogna eseguire la prima passata (-R 1) durante la quale viene salvato il file ''**divx4.log**'':

<code>
transcode -i stream.yuv -R 1 -y xvid -o /dev/null
</code>

Poi si esegue la seconda passata a bitrate variabile (-R 2), video encoder bitrate 6000 and keyframes every 250 frames (-w), formato audio mp3 (-N 0x55) encoder bitrate kBits/s (-b 96). Contestualmente si effettua il deinterlacing con il filtro //smartyuv//:

<code>
transcode -i stream.yuv \
    -J smartyuv=highq=1:diffmode=2:cubic=1:Blend=1:chromathres=4:threshold=8:doChroma=1 \
    -R 2 -w 6000,250 -y xvid \
    -V \
    -N 0x55 -b 96 \
    -o output.avi
</code>

===== Converting from Flash Video to XviD =====

Mplayer supports a very large set of video formats, including several closed codecs from the Windows platform. Using the **[[http://www.arrakis.es/~rggi3/youtube-dl/|youtube-dl]]** script, we downloaded some clips from [[http://www.youtube.com/|YouTube]], which are in the Flash Video format.

The first, very simple recipe uses **''mencoder(1)''** to convert a **Macromedia Flash Video** to **XviD/MP3 AVI** in a single pass, with fixed bitrate (360 kbit/s in this example):

<code bash>
mencoder file.flv -oac copy -ovc xvid -xvidencopts bitrate=360 -of avi -o file.avi
</code>

The output audio codec is ''**copy**'' because flv should be already in mp3 format, otherwise we can specify something like **''%%-oac mp3lame -lameopts br=96:cbr%%''**.

An insanely complicated recipe will use **mplayer to extract** the video and audio streams, then use **transcode to convert** the video to XviD (two pass, 400 kbit):

<code>
FILE=youtube_clip
mplayer -ao pcm:file=$FILE.wav -vo yuv4mpeg:file=$FILE.yuv $FILE.flv
transcode -i $FILE.yuv -R 1 -w 400 -y xvid -o /dev/null
transcode -i $FILE.yuv -R 2 -w 400 -y xvid -o $FILE.xvid
rm $FILE.yuv divx4.log
</code>

Finally we used **avidemux** to convert audio to mp3 and to mux audio and video into an avi file. FIXME How to use transcode for this final step?

===== Estrarre audio nellymoser da un Flash Video =====

Un video .flv con audio in formato //nellymoser// si ascolta correttamente con mpalyer, ma l'audio estratto con **''mplayer -dumpaudio''** oppure con **''avidemux''** non viene riconosciuto ed è impossibile ascoltarlo. Per fortuna **''ffmpeg''** è in grado di effettuare l'estrazione e la conversione automaticamente:

<code>
ffmpeg -i video.flv output_audio.wav
</code>

===== How to extract subtitles from a DVD-Video into VobSub format =====

See this paragraph: **[[ripping_dvds_with_mencoder#subtitles|Ripping DVDs with mencoder - Subtitles]]**.

===== avisync =====

This is a tool that allow to adjust audio/video syncronization witout re-encode audio and video streams, you must specify time shift in frames. If count is positive, audio starts with audio frame count at the beginning of the AVI-file. If count is negative, audio is prepended count padding frames.

<code>
avisync -i input.avi -o output.avi -n -10
</code>

===== Converting AC3 audio to WAV =====

AC3 audio (aka Dolby Digital) is a **lossy** compression algorithm, so converting from and to this format **always introduces some more loss**. Neverthless I had to edit a DVD audio track with Audacity, so I need to convert it from AC3 into something that Audacity can open. The ac3 audio track was extracted with **[[mplayer|mplayer]]** and the **-dumpaudio** option.

<code>
transcode -i title1.ac3 -y null,wav -o title1.wav
</code>