[FFmpeg-user] Filter just the 1st audio channel of the input.

[Jim]

On 2/3/21 7:40 AM, Marco Mircoli wrote:
> Hello,
>     wandering if it is possible to process just the 1st audio channel of an
> input.
> I don't know how many channels I will have as input, but I know that I have
> to process just the 1st and the others I have not to considerate.
>
> INPUT from mono to multichannel
> filters.....
> OUTPUT just one channel (mono)
>
> I've tried this but doesn't works
>
> ffmpeg -i FILE_FROM -map_channel 0.0.0 -af
> highpass=f=70,adeclick,loudnorm=I=-16.5:TP=-1.5:LRA=7 FILE_TO
>
> Any suggest?
> Thanks.
> S.
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I do not know what you're specifically trying to accomplish with this, 
but I have a script in which I need to reduce videos with an unknown 
number of channels into 2.  How I accomplished it was to dump the audio 
to a stereo wave file, run some external processing on it, then 
multiplex it back with the original video while encoding it as a stereo 
MP3 audio track.  If you cannot find a better solution, perhaps 
something similar would work for your purpose, only using -ac 1 instead 
of -ac 2 as I do?

Just an idea.

Jim