[FFmpeg-devel] [PATCH 000/279] New channel layout API

[James Almer]

On 12/14/2021 10:03 AM, Nicolas George wrote:
> James Almer (12021-12-13):
>> Can't user defined names let you do that without the need to reuse the same
>> AVChannel value in a given layout? And for that matter, can you not set said
>> names within the filter itself and not in the layout?
> 
> I do not see how they could. But as always, "I do not see how" is not an
> argument, it only points to my limitations. So if you do know, please
> let me know.

You have a stream with four channels, you set up a custom order layout 
where you pick any four unused ids and call them OboeFL, OboeFR, 
PianoFL, PianoFR in u.map[], then split the streams (retaining strings 
and ids), pass them to channelmap using 
channelmap=map=OboeFL-FL|OboeFR-FR once support is added an so on. Or am 
i missing something?

> 
> But I suspect we are talking at cross-purposes here. You say “the
> filter”, singular, but the issue is not an isolated filter, the issue is
> about several components working together in harmony. For example a
> demuxer that knows about exotic layouts and labels such, but later a
> filter that does not and only knows about standard channel identifiers.
> 
>> Mapping a channel (each of the data pointers in a frame) to an specific
>> output, like a speaker.
> 
> I think this definition is too narrow. Currently, channel layouts are
> also used to compute matrix coefficients for remixing, for example.
> 
> But even if we adopt this definition, mapping (oboe left, oboe right,
> piano left, piano right) onto stereo is perfectly in scope.
> 
> Regards,
> 
> 
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