Filter just the 1st audio channel of the input.

[Marco Mircoli]

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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[Paul B Mahol]

On Wed, Feb 3, 2021 at 2:05 PM Marco Mircoli <[hidden email]> 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
>

you will need to extract each channel by channelsplit filter, and later
merge it with other filters.
This makes filtergraph description longer.
Some filters support processing only specific channel but most do not as it
does not make sense for such filters.

>
> Any suggest?
> Thanks.
> S.
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[Ruler2112]

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.
> _______________________________________________
> ffmpeg-user mailing list
> [hidden email]
> https://ffmpeg.org/mailman/listinfo/ffmpeg-user
>
> To unsubscribe, visit link above, or email
> [hidden email] with subject "unsubscribe".

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
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[Nicolas George]

Marco Mircoli (12021-02-03):

>    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

Just use pan=mono|c0=c0 to extract the channel you want wherever you
want in the graph.

No need to completely split the channels, it was meant for versions that
lack the pan filter.

Regards,

--
  Nicolas George

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[Paul B Mahol]

On Wed, Feb 3, 2021 at 7:48 PM Nicolas George <[hidden email]> wrote:

> Marco Mircoli (12021-02-03):
> >    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
>
> Just use pan=mono|c0=c0 to extract the channel you want wherever you
> want in the graph.
>
> No need to completely split the channels, it was meant for versions that
> lack the pan filter.
>

You missed fact that user needs all channels again, not just first.

>
> Regards,
>
> --
>   Nicolas George
> _______________________________________________
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