[FFmpeg-devel] [PATCH v3 3/3] avcodec/aacdec: Translate PCE to avutil channel layouts

Alex Converse alex.converse at gmail.com
Thu Oct 25 01:16:43 EEST 2018


On Wed, Oct 24, 2018 at 1:03 PM pkv.stream <pkv.stream at gmail.com> wrote:
>
> Patch updated ; passes all FATE tests.
>
> Comments from Alex Converse review incorporated (much thanks to him).
>

Hey,

I'm a bit concerned with the outputs this generates for low channel
count streams.

al17_44.mp4 has two front SCEs.

"ISO/IEC 13818-7:2005(E), 8.5.3.2 Explicit channel mapping using a
program_config_element" says:

Included in the PCE are “list of front channels”, using the rule
center outwards, left before right. In this list, a center channel
SCE, if any, must come first, and any other SCE’s must appear in
pairs, constituting an LR pair. If only two SCE’s are specified, this
signifies one LR stereophonic pair.

Before the patch we were getting L+R. With the patch we are getting
(FC+TFC) (0x2004).

I know of at least one commercial encoder that supports unpaired dual mono.

Do you know which spec the contains the eratta for top channels? There
doesn't seem to be much of value in Amd.6. Do you have any real
examples of a multichannel stream with a top center speaker or any
supporting documentation you could point me at?

Thanks,
Alex


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