[FFmpeg-user] AC-3 encoding questions

[Thomas Worth]

On Tue, Nov 1, 2011 at 9:04 AM, Carl Eugen Hoyos <cehoyos at ag.or.at> wrote:
> Thomas Worth <dev <at> rarevision.com> writes:
>
>> I'm trying to encode some 6 channel, 24-bit WAV files, but am getting
>> some warnings from FFmpeg:
>>
>> [ac3 @ 0x101920200] channel_layout not specified
>
> (Complete, uncut output missing.)
>
> If the wav file really has no channel layout specified, the ac3 encoder will
> guess the layout (and says so if I am not wrong) as 5.1.
> Only specify a layout if you don't like what the encoder guesses.

Hi Carl. Sorry, here's full output. Obviously the channel layout is
wrong, but you get the idea:

macpro:AUDIO user$ ffmpeg -i Reel_02_0999.wav -vn -acodec ac3 -ab 320k
-ac 6 -channel_layout 120 -y Reel_02_TEST.ac3
ffmpeg version 0.8.5.git, Copyright (c) 2000-2011 the FFmpeg developers
  built on Oct 20 2011 02:47:48 with gcc 4.2.1 (Apple Inc. build 5666) (dot 3)
  configuration: --disable-doc --enable-static --disable-shared
--enable-gpl --enable-nonfree --enable-version3 --enable-libfaac
--enable-libx264 --enable-libvpx --enable-libmp3lame --cc=gcc-4.2
--enable-pthreads --arch=x86_64 --target-os=darwin
--extra-cflags='-I/sources/faac-1.28/include -I/sources/libvpx
-I/sources/lame-3.98.4 -I/sources/x264 -isysroot
/Developer/SDKs/MacOSX10.6.sdk -mmacosx-version-min=10.6'
--extra-ldflags='-L/sources/faac-1.28/libfaac/.libs -L/sources/libvpx
-L/sources/lame-3.98.4/libmp3lame/.libs -L/sources/x264 -isysroot
/Developer/SDKs/MacOSX10.6.sdk -mmacosx-version-min=10.6'
  libavutil    51. 22. 0 / 51. 22. 0
  libavcodec   53. 22. 0 / 53. 22. 0
  libavformat  53. 17. 0 / 53. 17. 0
  libavdevice  53.  4. 0 / 53.  4. 0
  libavfilter   2. 44. 1 /  2. 44. 1
  libswscale    2.  1. 0 /  2.  1. 0
  libpostproc  51.  2. 0 / 51.  2. 0
[wav @ 0x101805800] parser not found for codec pcm_s24le, packets or
times may be invalid.
[wav @ 0x101805800] max_analyze_duration 5000000 reached at 5003458
Input #0, wav, from 'Reel_02_0999.wav':
  Duration: 00:16:53.22, bitrate: 6912 kb/s
    Stream #0:0: Audio: pcm_s24le ([1][0][0][0] / 0x0001), 48000 Hz, 6
channels, s32, 6912 kb/s
Incompatible sample format 's32' for codec 'ac3', auto-selecting format 'flt'
[ac3 @ 0x101920200] Specified channel_layout is not supported
Output #0, ac3, to 'Reel_02_TEST.ac3':
    Stream #0:0: Audio: ac3, 48000 Hz, 6 channels (LFE|BL|BR|FLC), flt, 320 kb/s
Stream mapping:
  Stream #0.0 -> #0.0 (pcm_s24le -> ac3)
Error while opening encoder for output stream #0.0 - maybe incorrect
parameters such as bit_rate, rate, width or height