Let user specified input audio codec and not relay on the default one

[Kazhuu]

This PR relates to this #702 issue I posted earlier. This let user to specify input audio codec to be used instead of relaying on FFMPEG default one. Default codec is PCM_S16LE and in one scenario I needed to specify PCM_S32LE instead.

Some questions still on my head related to this:

• I only added PCM codecs. Is this okay? I think in the future if someone needs more they can be added quite easily.
• Anything to improve here? I'd be happy to modify this PR if needed.

With this change av.open can for example be called with

import av
av.open('alsa_device_name', format='alsa', audio_codec='PCM_S32LE')

[jlaine]

Could we have some unit tests for this please?

Also the docstring should clarify what the usecase for this is: AFAICT this only makes sense for reading from audio devices (ALSA + pulse).

[Kazhuu]

@jlaine do you think it would make sense to add documentation or something to list the supported codecs? I added a simple test but was thinking could I somehow test the default codec somehow when the audio_codec is not given. I couldn't find tests that open any alsa devices.

[WyattBlue]

I'm closing this because this PR needs to be redone. It has merge conflicts and uses an old code style, (we prefer double quotes now).

I don't know if jlaine would agree with me but I think av.open("alsa_device_name", format="alsa:pcm_s32le") would be a better interface, (the parsing would be implemented in PyAV). I would think along these lines if you were to redo this.

For me, this is a very low priority feature. It's probably a low priority for jlaine too. I don't know anyone else who needs this. I wouldn't it if it were to be implemented, but it would need to be done in another PR.

[Kazhuu]

Hello @WyattBlue. Thanks for commenting on this one. I don't really need this feature anymore so I don't see myself working on this PR again, also because the process has been quite slow I always forgot what I did last time. So this can be closed and the issue I opened also be closed. Maybe someone else who also needs this can find this and continue the work. Thanks for you time!