[FFmpeg-devel] [PATCH] rematrix DPLII fix for channel downmixing. Surround now adds to front rather than taking away.

Michael Niedermayer michaelni at gmx.at
Sat Mar 15 19:00:37 CET 2014

On Sat, Mar 15, 2014 at 05:51:09PM +0100, Hendrik Leppkes wrote:
> On Sat, Mar 15, 2014 at 4:46 PM, Peter Robertson
> <Peter at corrosivetruths.org> wrote:
> > This fixes a problem where trying to convert gameplay sound to Dolby Pro
> > Logic II would result in a left channel that would be missing the sounds
> > that were in center and back left at the same time. I also applied it to
> > Dolby Pro Logic as it should work the same way. Sorry if I've done
> > anything wrong, first patch. Fixes #3455
> >
> The encoding matrix for DPL/DPLII is defined by Dolby, and only sounds
> good if you use a DPL compatible decoder to reconstruct the original
> signal.
> Its not necessarily supposed to be played as stereo through stereo speakers.
> All Information I could find about DPL encoding suggests that the
> implementation is correct as it is today. Left channel subtracts both
> surrounds, and right channel adds them.

The EAC-3 specs suggested downmix also seems to match this

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

If a bugfix only changes things apparently unrelated to the bug with no
further explanation, that is a good sign that the bugfix is wrong.
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