[mythtv] [mythtv-commits] Ticket #1104: multichannel audio support

[Mark Spieth]

> Cheers, Mark - Patch 38 has fixed the audio echo and the upmix sounds
> great. Is the channel balance configurable anywhere? I could do with
> increasing the rear channel levels a little.

play with params.dimension in FreeSurround constructor.
0..100 moves the soundfield backwards. 0 is default.
perhaps a number > 0 for music mode is warranted. Ill let others decide as 
my 5.1 setup has the rears at the side as the wires arent long enough to go 
far.
center_width is similar. 0 is all centre energy is in centre. 100 is all in 
l/r and none in centre (I think)
I chose 50 for music mode and 0 for movie mode. Opinions on music mode 
choice?

Should these be tunable in settings for both modes?

> 2007-12-28 12:44:09.871 AFD: Selected track 1: English LIBA52 5.1ch (A/V
Stream #1)
> 2007-12-28 12:44:09.871 AFD: Initializing audio parms from audio track #1
> 2007-12-28 12:44:09.871 AFD: Audio format changed
>                         from id(NONE)    -1Hz -1ch   0bps    ;
> id(NONE)    -1Hz -1ch   0bps
>                         to   id( AC3) 48000Hz  6ch  16bps    ; id( AC3)
> 48000Hz  6ch  16bps
> The new upmixer is so good, I can't tell whether this is actually using
> the original 6-channel audio or upmixing! I noticed the 'Needs upmix'
> message, despite the device having 6 ch and the source the same. Must
> try and find a DVD with better channel separation to try!

6ch is only swapped s that they come out the correct channel. no real upmix 
is done though it uses the library to do this.
upmix is only done on 2ch audio. 4ch audio is not currently handled. unsure 
as to the best alternative is for this but Ive never seen a 4ch audio track. 
Ill handle it when someone complains. :-)
use a SD 2ch soundtrack. or any 2ch AVI. they sound great compared to 
passive mode.

The major difference in passive mode between the previous incarnation and 
this one is that stretch is done in 6ch instead of 2ch so may be slightly 
worse performance wise for those with gutless 6ch out systems (sorry adam)

I also see you still use liba52. any reason why?
obviously works though so it is a good test. Ive only rtied with internal 
ac3 dec.

> Thanks for working on this patch, Mark, it's definitely something that
> Myth's been waiting for...

as soon as I found freesurround, I had to add it. couldnt resist. I had been 
looking for a way to use an existing win lib for dpl2 which this guy did too 
but he was disappointed in its quality so he wrote his own. dont know how to 
contact him though.

also for the devs, any problems let me know before 7 jan so I can fix it in 
reasonable time.
el_surround.cpp is an original file but I have altered it significantly 
functionally for lfe and performance.
I can reformat to the standard or let it stand as partially original and 
partially correct.

mark