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

[pehache]

Le 28/01/2019 à 23:58, pehache a écrit :
> 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 ?

Just checked, the output of:

ffmpeg -i test.mkv -map 0:1 -af
aresample=matrix_encoding=dplii -t 300 a.wav

is bit to bit identical to:

ffmpeg -i test.mkv -map 0:1 -t 300 a.wav

So "aresample=matrix_encoding=dplii" doesn't apply any encoding by 
itself, it just sets the downmixing parameters that are applied by "-ac 2" ?