[Libav-user] FFmpeg channel layouts

rohit khali khali.rohit at gmail.com
Thu Jul 21 19:55:32 EEST 2022

Thanks Nicolas,
As always your response answers my question. So it's confirmed that in our
E-AC3 example FFmpeg does change the order of decoded channels when
compared to the channel order illustrated by acmod values in the encoded
bitstream. Let's keep the channel ordering aside for the below part.

Channel layout and naming conventions have always been a topic with some
doubts for me. For example: In this case, FFmpeg reported channels are "FL
FR FC LFE SL SR" while as per ATSC A/52 channels are "L, C, R, Ls, Rs,
LFE". Now if we see, as per R-REC-BS.2051-3 both FL(M+060) and L(M+030) are
different. Even while measuring the loudness, channel weights are different
for both FL and L.
This difference is one of the main reasons I rely on deriving/reporting
channel layout with names as per corresponding standard. But since the
decoder is FFmpeg, I have to map extracted information from the encoded
bitstream parsing with the FFmpeg decoded one.

Any guidance on these naming conventions will also be helpful for me.

Rohit Khali
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