Feature request: save audio as mono

[lockheed]

This option is lacking and I think it is very important for those who download lectures or talk shows from youtube.

Stereo there is useless, and saving a file as mono makes the file size two times smaller.
Also, some lecture videos have good sound only on one channel, while the other remains nearly silent, which is quite annoying when listening. This function would get rid of that, too.

I think it is definitely worth implementing.

[KaelosBeren]

FFmpeg supports the conversion of stereo to mono:

https://trac.ffmpeg.org/wiki/AudioChannelManipulation

Is this possible with youtube-dl?

[lborgman]

Some speech recognition API requires mono so this would be very convenient.

[musiclandUSA]

I would very much like this feature as well, I'm ripping a recorded live show for podcast and would like to dump stereo so we can use a 32kbps aac bitrate. Anyone figured this out in the last 6 months?

Might have answered my own question on this one:

youtube-dl --extract-audio --audio-format mp3 --audio-quality 64 --postprocessor-args "-ac 1" makes a 64kbps mono mp3 file. Only thing I'm unable to do is make a 32kbps mono aac file, youtube-dl seems to ignore the --audio-quality setting for aac.

https://trac.ffmpeg.org/wiki/AudioChannelManipulation

[Neurognostic]

I have a use case. For some (rare) videos that have very poor or no audio at all in one of the stereo channels, it would be great to be able to select a channel and use mono instead.

As a workaround this su answer offers two options for converting a stereo video into mono:
https://superuser.com/a/1063242

ffmpeg -i input -map_channel 0.0.0 output

or

ffmpeg -i input -af "pan=mono|c0=FL" output

These both worked for me after youtube-dl had finished post-processing.

I tried using --postprocessor-args but wasn't able to get youtube-dl to pass them correctly to ffmpeg.

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Edit;
A bonus would be a flag for automatically detecting an empty[/quiet] channel and converting to mono automatically. Not sure if any of the current [optional] dependency can do that sort of thing.