[FFmpeg-user] stereo upmix and matrix_encoding

[Martin Thomas Schrott]

> That should not be needed at all.


yes, that is, what the documentation also said. I had -ac2 in front - 
maybe this caused the problem. But I had thought this would tell, that 
the original file has two channels - instead -ac2 in front of surround 
tells surround to use two channels as output - not sure, if this is, 
what -ac normally means :-/



> But only logs would show what really happens.


the logs did show me this ;-) i used --loglevel debug on ubuntu to get 
more details on what happened.

As I read in the logs, that the output of surround was set to stereo I 
got the idea that -ac 2 could cause it and changed it to -ac 6 - maybe 
removing it would also have done the trick - but this way it should be 
safe, even if the default changes :-)

Anyway - for me it is strange that -ac 2 does change the output of 
surround - as surround has its own attributes to configure the output.


> thanks!
>
> Martin
>
>
>
> Am 16.06.2023 um 13:51 schrieb Martin Thomas Schrott:
>>> Hi folgs,
>>>
>>>
>>> I would like to upmix a stereo file to a surround one and came accross
>>> the "surround" filter in ffmpeg documentation. Seems this does what I
>>> would like to do, but I could not find how to use it correctly as it
>>> seems.
>>>
>>>
>>> I would like to combine it with aresample=matrix_encoding=dplii to get
>>> a correct surround wav out.
>>>
>>>
>>> So I tried to use a -filter_complex with my stereo as an input file.
>>>
>>> And send the output from surround to aresample for encoding.
>>>
>>>
>>> -i myfile.wav -filter_complex "[0:a]surround[a1];
>>> [a1]aresample=matrix_encoding=dplii" outfile.wav
>>>
>>>
>>> The file still is normal stereo and ignored by decoders. :-(
>>>
>>> I also tried to add ichl=5.1 to the aresample - which also did not help.
>>>
>>>
>>> Could anyone please either tell me, what I am doing wrong,
>>>
>>> or give me another working way to upmix the file and encode it correctly?
>>>
>>>
>>> (I know this way the phaseshift is missing - so if someone could
>>> include that too, I would appreciate that of course) ;-)
>>>
>>>
>>> If combining does not work properly I also would be fine with
>>> outputing a six channel wav or six separate wave files, as I have the
>>> code to encode this correctly. :-)
>>>
>>>
>>> Thanks for any hint and help!
>>>
>>>
>>> cheers
>>>
>>> Martin
>>>
>>>
>>>
>>>
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