[MPlayer-users] Re: Quicktime sound atom v2: Wrong audio channel mapping

[Corey Hickey]

Frank Aurich wrote:
> Frank Aurich wrote:
> 
>>Hi,
>>
>>with the recent fix by Corey Hickey, new Apple Quicktime videos which 
>>use the sound atom 2 (e.g. HD trailers) play fine in MPlayer.
>>The audio channel mapping, however is wrong on 5.1 sound systems.
>>
>>The speech channel, which should come from the center speaker, is mapped 
>>to front left. I dont know about the others, mainly because it's 
>>difficult to determine ;)
>>
>>Tested with latest mplayer-cvs and the following trailers:
>>
>>http://movies.apple.com/movies/universal/king_kong/king_kong-tlr_h720p.mov
>>http://movies.apple.com/movies/wb/superman_returns/superman_returns-tlr1_h720p.mov 
>>
>>
>>
>>Frank Aurich
> 
> 
> Can anybody confirm the described behaviour on their system or is it a 
> problem on my side?
> 
> I figured I could simply remap the channels by using the -channels 
> option, but for that I'd first need to know the wrong mapping.
> I was wondering therefore if anyone has a AAC audio or MP4 video file 
> which uses Quicktimes sound atom 2, that clearly advertises each of the 
> 5 (or 6) channels (i.e. some test signal that simply puts a singular 
> sound to each of the speakers).

The channel mapping is documented on Apple's website. I always have a
hard time finding it:

http://developer.apple.com/documentation/MusicAudio/Reference/CACoreAudioReference/CoreAudioTypes/Enums/Enums.html

The corresponding line is, I think:

kAudioChannelLayoutTag_AAC_5_1 = kAudioChannelLayoutTag_MPEG_5_1_D, // C
L R Ls Rs Lfe

...which means:

0 - center front
1 - front left
2 - front right
3 - rear left
4 - rear right
5 - lfe

As far as I know, mplayer always assumes the channel mapping is like the
AC3 5.1 stored in DVDs:

0 - front left
1 - front right
2 - rear left
3 - rear right
4 - center front
5 - lfe

So, the remapping would be like this:
-af channels=6:5:0:4:1:0:2:1:3:2:4:3

...and manually downmixing to 2 channels would be like this:
 -af pan=2:0.4:0.4:0.4:0:0:0.4:0.2:0:0:0.2:0.5:0.5

Note that the relative mixing levels in the above line are mostly
arbitrary, and I can't practically test either of them because I don't
have a surround setup. Starting from here, though, you ought to be able
to correct any mistakes I made.

One of these days I'll probably get around to figuring out how to fix
mplayer so it understands the correct channel mapping. Of course, if
anybody else wants to do it, feel free.

-Corey