[FFmpeg-user] channel layout for raw pcm16le audio

[Steve Kenton]

I'm trying to understand a problem I'm having reading raw stereo pcm16le 
audio from a fifo. The channel_layout I specify seems to be ignored and 
always "guessed"  and it always reads 5 seconds of data to probe the 
format even though I think I've specified everything.

The example below uses /dev/zero instead of a fifo as a simple test 
case. When using real audio data it hangs for 5 seconds or so during the 
probe.

Any idea how to specify the input so completely that the probe can be 
skipped?

Thanks - Steve Kenton


~$ ffmpeg -f s16le -sample_rate 48000 -channels 2 -codec:a pcm_s16le 
-channel_layout stereo -i /dev/zero -f s16le -codec:a pcm_s16le -y xxx.pcm
ffmpeg version git-2013-01-17-c345100 Copyright (c) 2000-2013 the FFmpeg 
developers
   built on Jan 16 2013 20:52:04 with gcc 4.6 (Ubuntu/Linaro 4.6.3-1ubuntu5)
   configuration: --enable-gpl --enable-libass --enable-libfaac 
--enable-libfdk-aac --enable-libmp3lame --enable-libopencore-amrnb 
--enable-libopencore-amrwb --enable-librtmp --enable-libtheora 
--enable-libvorbis --enable-libvpx --enable-x11grab --enable-libx264 
--enable-nonfree --enable-version3
   libavutil      52. 15.100 / 52. 15.100
   libavcodec     54. 89.100 / 54. 89.100
   libavformat    54. 60.101 / 54. 60.101
   libavdevice    54.  3.102 / 54.  3.102
   libavfilter     3. 32.100 /  3. 32.100
   libswscale      2.  1.103 /  2.  1.103
   libswresample   0. 17.102 /  0. 17.102
   libpostproc    52.  2.100 / 52.  2.100
[s16le @ 0x2b64340] max_analyze_duration 5000000 reached at 5013333 
microseconds
[s16le @ 0x2b64340] Estimating duration from bitrate, this may be inaccurate
Guessed Channel Layout for  Input Stream #0.0 : stereo
Input #0, s16le, from '/dev/zero':
   Duration: N/A, bitrate: 1536 kb/s
     Stream #0:0: Audio: pcm_s16le, 48000 Hz, stereo, s16, 1536 kb/s
Output #0, s16le, to 'xxx.pcm':
   Metadata:
     encoder         : Lavf54.60.101
     Stream #0:0: Audio: pcm_s16le, 48000 Hz, stereo, s16, 1536 kb/s
Stream mapping:
   Stream #0:0 -> #0:0 (pcm_s16le -> pcm_s16le)
Press [q] to stop, [?] for help
size= 1735584kB time=02:34:16.44 bitrate=1536.0kbits/s
video:0kB audio:1735584kB subtitle:0 global headers:0kB muxing overhead 
0.000000%