[MPlayer-dev-eng] [PATCH] Automatic downmix

[Nicolas George]

Le decadi 30 thermidor, an CCXVIII, ubitux a écrit :
> Are those quotients arbitrary?

Mostly.

>				 There is an overflow of 20% with this, is
> it normal? I tried to keep them summing up to 1.0, was I wrong? Still my

You have to forgive me, I have not finished my math PhD, so summing six
number is still a bit beyond my league.

> values are totally arbitrary, so maybe we should correct them.

I looked at how ffac3 does it, and it redirected me to the AC3 spec (look
for '"Downmixing Into Two Channels" -ffmpeg' in Google). The values are
variable among a few fixed values. Taking average values gives something
like:

L = 0.48 FL + 0.28 FC + 0.24 RL  (and idem for R)

That is for 5 channels. For 5.1, the LFE channel can have any gain between
+10 and -21 dB. The values you chose are quite similar.

Anyway, the exact values probably make less difference than sitting a few
rows more to the front or to the rear in the theater.

> Also, you may have notice my patch make the values still readable:
> 
>   "0.4:0:"      // Front left
>   "0:0.4:"      // Front right
>   "0.2:0:"      // Back left
>   "0:0.2:"      // Back right
>   "0.3:0.3:"    // Center
>   "0.1:0.1"     // LFE

Nicely done.

Regards,

-- 
  Nicolas George
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