[FFmpeg-devel] [PATCH 1/5] avutil/channel_layout: add 22.2 layout

[Jan Ekström]

On Sat, Aug 1, 2020 at 3:08 PM Carl Eugen Hoyos <ceffmpeg at gmail.com> wrote:
>
> Am Sa., 1. Aug. 2020 um 14:06 Uhr schrieb Jan Ekström <jeebjp at gmail.com>:
>
> > Additionally, the spec only mentions stereo/5.1 for direct mapping, so
> > I've kept to 5.1 since we have the capability for that one.
>
> And you still believe it would be a disadvantage if the decoder outputs
> this 5.1 mapping by default if nothing else was requested?
>

Yes. API users so far have received the audio frames according to
encoded layout by default, so doing something else breaks that rule of
least surprises.

> Is there an option to request the 5.1 mapping?
>

As noted in the 0/0 cover letter, you can do it just fine with
`-channel_layout "5.1"` with ffmpeg.c. I have verified that it returns
the 5.1 channels as-is.

At this point I would not like to attempt to figure out how to skip
channel coding units in the AAC decoder, as swresample seems to handle
this nicely. So far the only usage for requested channel layout in
aacdec has been to skip reordering with AV_CH_LAYOUT_NATIVE , to
output the coded units as-is.

Best regards,
Jan