[MPlayer-dev-eng] [RFC] 6-channel AAC and channel reordering

[Corey Hickey]

Dominik 'Rathann' Mierzejewski wrote:
>>> I've tested it on my 4.0 setup and I didn't hear the front center and lfe
>>> channels until I downmixed it to 4ch:
>>> mplayer -af 
>>> pan=4:1:0:0:0:0:1:0:0:0:0:1:0:0:0:0:1:0.25:0.25:0:0:0.25:0.25:0:0 \
>>> return,_the_h720p.mov
>> That makes sense, since mplayer is outputting 6 channels, and on your 
>> system the last two aren't hooked up to anything. One thing, though: do 
>> you have channels=6 in your config file, or did you specify -channels 6 
>> on your command line? If not, then I'm confused, since as far as I know 
>> mplayer tells libfaad to downmix to 2 channels be default.
> 
> I have channels=4.

Ok, that'll do it too.

>> For some reason I have a nagging feeling that somebody else proposed a 
>> different approach and that it might have been committed, but I can't 
>> dig up the patch. Maybe I'm imagining things.
> 
> I can't recall any such thing.

Giacomo pointed out enough for me to go by. See the following, and lots
of replies in that thread.

To: mplayer-dev-eng at mplayerhq.hu
From: Alexander 'Lazy Ranma' Ponyatikh
Subject: [MPlayer-dev-eng] [PATCH] channel reordering for 6ch audio
Date: Sat, 29 Jul 2006 20:39:44 +0400

>> In any case, the patch I posted was mostly a proof-of-concept, but I 
>> guess it works. Looking back, I see two things I might do differently.
>>
>> (a) The chan_map array could just be a string, with creation of *int 
>> pointers for af->control happening right before they're needed. This 
>> would obviate the need for a separate af_set_channel_map() funcion.

That turned out to actually be messier, so I just changed it so the
function is only called in af.c instead of in each decoder.

>> (b) If (a) is done, then it would be easy to make sure the length of the 
>> array is as expected and prevent reading beyond the end.
>>
>> I'll go ahead and make those changes and see if it works.
> 
> Great. I guess nobody was interested because nobody who cared had access
> to >2ch speaker setup. Could you also take care of WMA? See the recent
> thread on -users for details.

I'm going to send an updated patch soon.

-Corey