[FFmpeg-user] aresample=matrix_encoding=dplii output is still 5.1 ??

[pehache]

Le 28/01/2019 à 14:11, Carl Eugen Hoyos a écrit :
> 2019-01-28 9:00 GMT+01:00, pehache <pehache.7 at gmail.com>:
>> Le 27/01/2019 à 16:53, Carl Eugen Hoyos a écrit :
>>> 2019-01-27 16:44 GMT+01:00, pehache <pehache.7 at gmail.com>:
>>>
>>>> I used to apply a Dolby Pro Logic II encoding this way :
>>>
>>> Actual command line and complete, uncut console output missing.
>>
>> ffmpeg -i test.mkv -map 0:1 -c:a aac -b:a 256k -af
>> aresample=matrix_encoding=dplii -t 300 a.m4a
> 
> You get stereo output with:
> -af aresample=matrix_encoding=dplii:out_channel_layout=stereo

OK. but what happens to the other channels (back and central) after the 
dplii encoding if out_channel_layout=stereo is not coded ? Are thay 
identical to the input ones or set to zero ?

> And identical output with -af aresample=matrix_encoding=dplii -ac 2

Since "-ac 2" performs a full downmixing according to the page I linked 
before, that means the others channels are zeroed ?

> Note that the dplii conversion does not do a correct phase shift,
> the output does not have optimal quality.

Do you mean in general with the DPLII principle, or specifically in ffmpeg ?