[FFmpeg-devel] [PATCH] aacenc: WIP support for PCEs

Kv Pham pkv.stream at gmail.com
Fri Nov 10 13:02:02 EET 2017

> Hi atomnuker,
> that's wonderful;
> there are two things also:
> 1) there are changes to make to the list of channel layouts not requiring
> ==> AV_CH_LAYOUT_5POINT0 to AV_CH_LAYOUT_5POINT0_BACK since the previous
> is 5.0(side) while the latter is 5.0 which is what is in spec (table 1.19
> ISO/IEC 14496-3:200X(E) or table 42 ISO/IEC 13818-7:2004(E) )
> see patch in attachment (can't be applied directly due to rebasing issues
> from your initial patch)
Checked the spec, you're right, fixed.

Great, you're right also about side being better than back in the commit

> 2) for everything to work I had to also apply the patch from here:
> http://ffmpeg.org/pipermail/ffmpeg-devel/2017-October/217357.html
> If you ffmpeg -loglevel debug , you will see that on non-default channel
> layouts, there is an auto insertion of a resampler filter : the
> channel_layout option is not passed correctly in the chain.
> for instance: ffmpeg -channel_layout octagonal -i input.wav -c:a aac
> -channel_layout octagonal out.mkv will matrix the input from octagonal to
> 7.1 before the encoding.
> Check ticket 6706 for details of the issue.
> I am not knowledgeable enough to be sure my fix is correct; it's working
> for sure, but I've had very few feedback (only Michael and Moritz about
> styling issues).

Pining Michael to take a look at it.

Discussing this with Michael.
My patch fails when there is down or upmixing.
I think there are at least two bugs hiding one behind another within the
filter chain.
It's a pity because this cripples your PCE implementation to ffmpeg default
channel layouts only (2.1 4.0 5.0 5.1 6.1 7.1 hexadecagonal), where 4.0 5.0
5.1 7.1 do not require PCE anyway.
I'll try to find a solution but senior dev help might be needed because
this is quite convoluted.


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