[FFmpeg-devel] Formats with 0 channels

[Andreas Öman]

Hi

Some streams have the AAC channel configuration stored as a PCE
element inside the stream, but sample rate can be recovered
from format.

This causes ffmpeg to believe that it should use 0 channels
for output:

$ ./ffmpeg_g  -i samples/aac_lc/al03_48.mp4 -f s16be /dev/null
FFmpeg version SVN-r13618, Copyright (c) 2000-2008 Fabrice Bellard, et al.
   configuration:
   libavutil version: 49.7.0
   libavcodec version: 51.57.0
   libavformat version: 52.14.0
   libavdevice version: 52.0.0
   built on Jun  2 2008 08:44:21, gcc: 4.1.3 20070929 (prerelease) 
(Ubuntu 4.1.2-16ubuntu2)
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'samples/aac_lc/al03_48.mp4':
   Duration: 00:00:08.23, start: 0.000000, bitrate: 67 kb/s
     Stream #0.0(und): Audio: aac, 48000 Hz, 0 channels
File '/dev/null' already exists. Overwrite ? [y/N] y
Output #0, s16be, to '/dev/null':
     Stream #0.0(und): Audio: pcm_s16be, 48000 Hz, 0 channels
Stream mapping:
   Stream #0.0 -> #0.0
Press [q] to stop encoding
Floating point exception (core dumped)

The attached patch fixes this by checking for both a valid
sample rate and number of channels, i.e:

$ ./ffmpeg_g  -i samples/aac_lc/al03_48.mp4 -f s16be /dev/null
FFmpeg version SVN-r13618, Copyright (c) 2000-2008 Fabrice Bellard, et al.
   configuration:
   libavutil version: 49.7.0
   libavcodec version: 51.57.0
   libavformat version: 52.14.0
   libavdevice version: 52.0.0
   built on Jun  2 2008 08:44:21, gcc: 4.1.3 20070929 (prerelease) 
(Ubuntu 4.1.2-16ubuntu2)
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'samples/aac_lc/al03_48.mp4':
   Duration: 00:00:08.23, start: 0.000000, bitrate: 67 kb/s
     Stream #0.0(und): Audio: aac, 48000 Hz, mono
File '/dev/null' already exists. Overwrite ? [y/N] y
Output #0, s16be, to '/dev/null':
     Stream #0.0(und): Audio: pcm_s16be, 48000 Hz, mono, 768 kb/s
Stream mapping:
   Stream #0.0 -> #0.0
Press [q] to stop encoding
size=       0kB time=8.21 bitrate=   0.0kbits/s
video:0kB audio:770kB global headers:0kB muxing overhead -99.999873%
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