[Ffmpeg-devel] a52 and ffmpeg issue

Jim Dishaw list
Sun Oct 1 20:40:07 CEST 2006

Using the current source from the ffmpeg svn and the liba52 cvs I
encounter a problem with AC3 audio.  If I use -acodec copy, there is no
audio on playback.  If I transcode the audio to another codec, say MP3,
I get noise.

I tested the liba52 build by using the a52dec tool with the same input
file and successfully extracted the audio.  If I use the -acodec copy or
transcode with an input file that is encoded with something other than
AC3, ffmpeg works fine.  If I play the input file, the audio works fine.

My apologies if this is a rookie mistake--I tried searching for this
problem in the list, but did not find anything obvious.

Example command line

ffmpeg -i test.vob -vcodec copy -scodec copy -acodec copy -y test.mpeg

Example output

FFmpeg version SVN-r6398, Copyright (c) 2000-2004 Fabrice Bellard
  configuration:  --prefix=/opt/media --enable-mp3lame --enable-libogg --enable-vorbis --enable-a52 --enable-dts --enable-pp --enable-libgsm --enable-gpl --enable-shared --enable-a52bin --enable-pthreads --enable-faac --enable-faad --enable-gpl --extra-cflags=-I/opt/media/include --extra-ldflags=-L/opt/media/lib 
  libavutil version: 49.0.1
  libavcodec version: 51.16.0
  libavformat version: 50.5.0
  built on Oct  1 2006 02:16:07, gcc: 4.1.2 20060901 (prerelease)
  (Debian 4.1.1-13)

Seems that stream 0 comes from film source: 29.97 (30000/1001) -> 59.94 (60000/1001)
Input #0, mpeg, from 'test.vob':
  Duration: 00:00:13.5, start: 0.201589, bitrate: 6062 kb/s
  Stream #0.0[0x1e0]: Video: mpeg2video, yuv420p, 720x480, 9800 kb/s, 59.94 fps(r)
  Stream #0.1[0x80]: Audio: ac3, 48000 Hz, mono, 448 kb/s
Output #0, mpeg, to 'test.mpeg':
  Stream #0.0: Video: mpeg2video, yuv420p, 720x480, q=2-31, 9800 kb/s, 29.97 fps(c)
  Stream #0.1: Audio: ac3, 48000 Hz, mono, 448 kb/s
Stream mapping:
  Stream #0.0 -> #0.0
  Stream #0.1 -> #0.1
Press [q] to stop encoding
frame=  324 q=0.0 Lsize=    9848kB time=13.3 bitrate=6061.5kbits/s    
video:9076kB audio:726kB global headers:0kB muxing overhead 0.470353%

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