[MPlayer-users] 5.1 audio

[Corey Hickey]

Fredrik Eriksson wrote:
> Hello.
> I'm having problems understanding how 
> 5.1 audio works. I played around a 
> little with the channels audio filter, 
> and figured that on dvds the channels 
> are something like this:
> 
> 0 - left front
> 1 - right front
> 2 - left rear
> 3 - right rear
> 4 - front middle
> 5 - subwoffer
> 
> but some other files with 5.1 audio 
> (mostly matroska with aac) uses the 
> channels different, mostly they move the 
> middle speaker to channel 0 (I think 
> I've seen one where it was on 2 as well).
> 
> So question: Are the channels supposed 
> to be stored different in different 
> containers/codec? if so, wouldn't it be 
> a good idea to have mplayer detect the 
> container and add a filter chain so that 
> the audio is heard correctly?

Good question. Yes, the channel order is different in different types of
files. I don't know if there is any standard. MPlayer's internal channel
order is the same as 5.1 AC3 (like on DVDs), and any other ordering
causes MPlayer to output the channels in the wrong positions.

A few months ago I wrote a proof-of-concept patch to address this
situation for 6-channel AAC.

http://mplayerhq.hu/pipermail/mplayer-dev-eng/2006-February/040764.html

I didn't get any feedback, though, and I ended up moving on to other
things. I may take up the issue again later on if I have time (anyone
else is certainly welcome to do it for me, of course).

-Corey