[FFmpeg-user] stereo upmix and matrix_encoding

Martin Thomas Schrott list at mtsonline.at
Fri Jun 16 14:51:27 EEST 2023

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!



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