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

[Frank Aurich]

Corey Hickey wrote:
> 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

Thank you very much Corey, that did the trick perfectly.
An automatic recognition on MPlayer side would be nice, although, since 
it's only an issue with the hi-res trailers right now, it's not that big 
of deal to type it.
I load them in a batch most of the time anyway :)

Cheers,

Frank