ffmpeg audio/video dolby

ffmpeg-experiment-roku

Unfortunately, our mpeg demux is having problems parsing multiple audio streams out of a file and selecting the appropriate stream to play. We will enable the parsing of multiple audio streams in the future. 

There is a work around you can use today. If you have access to the content, you can strip the excess streams using a transcoding tool like ffmpeg: 

% ffmpeg -i MyMultiTracAudio.m4a 
.... 
Duration: 00:59:06.98, start: 0.000000, bitrate: 71 kb/s 
Stream #0.0(eng): Audio: aac, 44100 Hz, stereo, s16 
Stream #0.1(eng): Data: mp4s / 0x7334706D 
Stream #0.2(eng): Data: mp4s / 0x7334706D 
Stream #0.3(eng): Data: rtp / 0x20707472 

% ffmpeg -i MyMultitracAudio.m4a -map 0:0 MySingletracAudio.mp3 

% ffmpeg -i MySingletracAudio.mp3 
.... 
Input #0, mp3, from 'MySingletracAudio.mp3': 
Duration: 00:59:07.92, start: 0.000000, bitrate: 63 kb/s 
Stream #0.0: Audio: mp3, 44100 Hz, stereo, s16, 64 kb/s 

The -map option can map input streams to output streams. In this case I also transcoded the stream from aac to mp3. 

By default on Fedora, ffmpeg is not compiled against libfaac so the transcoding was a necessary step for me (libfaac is required for encoding aac). 

--Kevin
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RokuKevin
Roku Engineering
 
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Postby RokuKevin » Fri Jan 22, 2010 1:46 pm

Found another way to use ffmpeg to get an aac stream out without libfaac... You can copy a particular stream by specifying the audio codec as "copy". 

% ffmpeg -i MyMultiTracAudio.m4a -map 0:0 -acodec copy MySingleTracAudio.m4a 

% ffmpeg -i MySingleTracAudio.m4a 
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'MySingleTracAudio.m4a': 
Duration: 00:59:06.98, start: 0.000000, bitrate: 63 kb/s 
Stream #0.0(eng): Audio: aac, 44100 Hz, stereo, s16