[vlc-devel] AC3 3F1R downmix to stereo (simple downmixer)

[James Turner]

On 8 Sep 2009, at 11:04, Jean-Baptiste Kempf wrote:

> On Tue, Sep 08, 2009 at 10:46:13AM +0100, James Turner wrote :
>> I'm not at all happy with the symbolic name I chose for the layout
>> (AOUT_CHANS_4_CENTRE_REAR), feel free to pick a shorter/clearer/ 
>> better
>> name!
>
> What is it, like a 3.1 system?

Right, as defined at

	http://www.videolan.org/developers/vlc/doc/doxygen/html/a52_8h-source.html

(line 197, ish) it's
	{ 4, AOUT_CHAN_LEFT | AOUT_CHAN_RIGHT | AOUT_CHAN_CENTER |  
AOUT_CHAN_REARCENTER }, /* 3F1R 3/1 */

Apparently various other people have encountered the same issue I saw  
- lack of dialogue:

	http://forum.videolan.org/viewtopic.php?f=14&t=63607

I assume the format is optimised for efficient dubbing - all the music  
and effects are on the L/R channels, and all the dialogue is on the  
centre channel. Since the current simple downmix can't handle the  
format, VLC falls back to the trivial downmixer, which grabs the L/R  
channels and drops everything else.

>
>> Note this work was done on the 1.0 bugfix branch from git, since I
>> encountered compile errors with trunk (on Mac 10.5, XCode 3.1.3).
> This should be the same code.

Well, trunk failed on the vlc core libs, due to unused variables  
relating to #ifdef 0 teletext code (I forget the exact file and  
functions, since I am more interested in fixing the downmix issue)

Regards,
James