[MPlayer-users] AAC 5.1 and -af pan= (5.1ch->2ch)

Loren Merritt lorenm at u.washington.edu
Fri Feb 18 10:19:31 CET 2005

On Fri, 18 Feb 2005, LLoyd Bates wrote:

> Hi there,
> This message goes out to the people that use the pan filter and know
> exactly what they are doing.
> Up to now i wasn't able to fully enjoy a video encoded with 5.1 aac
> since mplayer did not downmix to Stereo. After some time i found the pan
> filter and played with it some time.
> This is what i found working: '-af
> pan=6:1:0:1:0:0:1:1:0:0.5:0.5:0.5:0.5'
> BUT, since i don't know exactly how to handle the pan filter the
> resulting Stereo output is less than optimal. Anyone out there that can
> give a better line for
> 5.1ch -> 2ch Stereo downmixing?
> (iirc this is only needed with aac 5.1. if the audio is ac3 or ogg
> vorbis mplayer will downmix automatically)
> and sorry for the bad english.

I use -af pan=6:.32:.39:.06:.17:-.17:.33:.32:.06:.39:-.17:.17:.33
I got the coefficients from MatrixMixer. I can't vouch for any theoretical 
basis, but they sound fine to me.
(You can see that my matrix is not normalized; I had to scale down the 
coefficients to avoid clipping.)

--Loren Merritt

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