[FFmpeg-user] stereo upmix and matrix_encoding

[Paul B Mahol]

On Fri, Jun 16, 2023 at 3:52 PM Martin Thomas Schrott <list at mtsonline.at>
wrote:

>
> > 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.
>
>
-ac 2 is output option, last time i checked.


>
> > 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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