How to manually set `mono` for the channel layout

[Michael Heuberger]

Summary of the bug:
When encoding the video, I always see this warning

Guessed Channel Layout for  Input Stream #1.0 : mono

I want this warning to disappear by manually setting the channel layout to mono. So that ffmpeg does not have to guess it. How can I do this? I did some research but didn't find such an option to manually set it. Can you add one?

How to reproduce:

% ffmpeg -r 14.563322542394877 -f image2 -i /home/michael-heuberger/binarykitchen/code/videomail.io/var/local/tmp/clients/videomail.io/11e4-686f-55c3c770-9cab-b5660842b8b4/frames/%d.jpg -i /home/michael-heuberger/binarykitchen/code/videomail.io/var/local/tmp/clients/videomail.io/11e4-686f-55c3c770-9cab-b5660842b8b4/videomail_preview.wav -y -acodec libfdk_aac -ar 44100 -ac 1 -vcodec libx264 -preset ultrafast -profile:v baseline -crf 24 -pix_fmt yuv420p -loglevel warning -movflags faststart /home/michael-heuberger/binarykitchen/code/videomail.io/var/local/tmp/clients/videomail.io/11e4-686f-55c3c770-9cab-b5660842b8b4/videomail_preview.mp4

$ ffmpeg   
ffmpeg version 2.4.2 Copyright (c) 2000-2014 the FFmpeg developers
  built on Oct 10 2014 15:15:58 with gcc 4.8 (Ubuntu 4.8.2-19ubuntu1)
  configuration: --extra-libs=-ldl --prefix=/opt/ffmpeg --enable-avresample --disable-debug --enable-nonfree --enable-gpl --enable-version3 --enable-x11grab --enable-libpulse --enable-libopencore-amrnb --enable-libopencore-amrwb --disable-decoder=amrnb --disable-decoder=amrwb --enable-libx264 --enable-libx265 --enable-libfdk-aac --enable-libvorbis --enable-libmp3lame --enable-libopus --enable-libvpx --enable-libspeex --enable-libass --enable-avisynth --enable-libsoxr --enable-libxvid
  libavutil      54.  7.100 / 54.  7.100
  libavcodec     56.  1.100 / 56.  1.100
  libavformat    56.  4.101 / 56.  4.101
  libavdevice    56.  0.100 / 56.  0.100
  libavfilter     5.  1.100 /  5.  1.100
  libavresample   2.  1.  0 /  2.  1.  0
  libswscale      3.  0.100 /  3.  0.100
  libswresample   1.  1.100 /  1.  1.100
  libpostproc    53.  0.100 / 53.  0.100
Hyper fast Audio and Video encoder

[Carl Eugen Hoyos]

To make this a valid ticket, please test current FFmpeg git head and provide a minimal command line (one that you made as short as possible still allowing to reproduce the issue you want to report) including the complete, uncut console output.

[Michael Heuberger]

Will do. But before I invest my time into this, let me know first if it's possible to manually set the channel layout to mono or not?

[Carl Eugen Hoyos]

Works fine here.

$ ffmpeg -channel_layout mono -f s16le -i /dev/zero
ffmpeg version N-67496-g715ccc2 Copyright (c) 2000-2014 the FFmpeg developers
  built on Nov 10 2014 01:54:33 with gcc 4.7 (SUSE Linux)
  configuration: --enable-gpl
  libavutil      54. 11.100 / 54. 11.100
  libavcodec     56. 12.100 / 56. 12.100
  libavformat    56. 12.103 / 56. 12.103
  libavdevice    56.  2.100 / 56.  2.100
  libavfilter     5.  2.103 /  5.  2.103
  libswscale      3.  1.101 /  3.  1.101
  libswresample   1.  1.100 /  1.  1.100
  libpostproc    53.  3.100 / 53.  3.100
Input #0, s16le, from '/dev/zero':
  Duration: N/A, bitrate: 705 kb/s
    Stream #0:0: Audio: pcm_s16le, 44100 Hz, mono, s16, 705 kb/s
At least one output file must be specified

As said, this is not a support forum, asking user questions here is not welcome and means asking for being flamed!

[Carl Eugen Hoyos]

Please reopen this ticket if you can provide a problematic command line including complete, uncut console output.