[MPlayer-advusers] liba52 downmixing

[Corey Hickey]

I'm trying to figure out what happens to the lfe channel of AC3 5.1
audio when liba52 is requested to downmix. Is the lfe discarded? Is it
mixed with the remaining channels? Is it reduced and then mixed?

I've dome my best to determine this experimentally but with all the 5.1
tracks I have I can't hear a difference in my two (front) speakers when
I switch between "-channels 5" and "-channels 6". Nor can I hear a
difference between "-channels 6" and "-channels 6 -af
pan=6:1:0:0:0:0:1:0:1:0:0:0:1": despite manually mixing the lfe channel
with the front channels, there's so much bass in the front channels
already that I can't hear the difference. Hence, my test is inconclusive.

I can hear a difference when I amplify the the lfe channel by using "-af
pan=6:1:0:0:0:0:2:0:1:0:0:0:2" (possible with a patch I just submitted
to mplayer-dev-eng), but that can't help me when a52 has already
downmixed and the lfe channel is no longer there.

I can't understand liba52/downmix.c. I've looked at it for a while and
haven't gotten anywhere. Can someone please enlighten me?

Thanks,
Corey