[FFmpeg-user] ffmpeg's Dolby Pro Logic feature is leaking center channel into surround channel

TBUFFestival tbuffestival at gmail.com
Fri Nov 27 23:49:13 CET 2015

From: Projection Journeyman

The full scope of my situation can be found here:


Including all things we have tried and why we need to do this, but just to
quickly summarize:

We are attempting to take a Dolby Digital .ac3 file we created from a
stereo file (left = left, right = right, center = mono of left+right, LFE
and surround sound are blank) and convert it to Dolby Pro Logic using
ffmpeg's aresample:

ffmpeg -i test-dolby-digital.ac3 -acodec libmp3lame -b:a 320k -af
"aresample=matrix_encoding=dplii" test-dolby-pro-logic.mp3

The center channel of the matrixed .mp3 comes out pretty good, but it is
leaking into the surround channel, even though we did not put anything at
all in the surround channel of the .ac3 file.  Can this be stopped?  We
don't see this in professionally rendered DPL soundtracks.  We did notice
there exists in ffmpeg aresample something called "surround_level" or
"slev" that can be set to zero but aren't sure if it applies here and even
if it does, how the syntax works and where it should be within the above
statement.  We also have our doubts it will even stop the leaking -- maybe
it is a byproduct of attempting to backconvert a stereo file into digital
and back to analog but matrixed?  But any idea anyone can come up with to
overcome this, even if it involves some software other than aresample or
ffmpeg for that matter would be greatly appreciated.

Projection Journeyman

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