Support multi channel PCM audio

[popcornmix]

Would be nice to support multichannel PCM output over HDMI, for example when decoding 6 channel AAC.

Requires firmware support in audio_mixer to handle arbritrary mixing of up to 8 input channels to up to 8 output channels.

[popcornmix]

Added in Hexxeh/rpi-firmware@ca3703d
Still needs plumbing in omxplayer.

You need to set config OMX_IndexConfigBrcmAudioDownmixCoefficients8x8 to audio_mixer.
The coeff is an array of 64 16.16 fixed point mixing coefficients.
The standard "dolby" 8 channel -> 2 channel matrix looks like:

   static const unsigned int coefficients_8[]= {
//input: FL     FR      C    LFE     SL     SR     RL     RR
      65536,     0, 46341, 46341, 46341,     0, 46341,     0,  // FL
          0, 65536, 46341, 46341,     0, 46341,     0, 46341,  // FR
          0,     0,     0,     0,     0,     0,     0,     0,  // C
          0,     0,     0,     0,     0,     0,     0,     0,  // SL
          0,     0,     0,     0,     0,     0,     0,     0,  // SR
          0,     0,     0,     0,     0,     0,     0,     0,  // LFE
          0,     0,     0,     0,     0,     0,     0,     0,  // RL
          0,     0,     0,     0,     0,     0,     0,     0,  // RR
   };

[bilditup1]

I'm glad someone's decided to pay attention to this! Thanks ppcrnmx!

[popcornmix]

First pass at multichannel PCM HDMI output has been pushed out.
Required updated firmware which is currently only on "next" branch.
sudo BRANCH=next rpi-update

use option "--layout 5.1" for example (2.0, 2.1, 3.0, 3.1, 4.0, 4.1, 5.0, 5.1, 7.0, 7.1 are the supported options).

Testers welcome.

[LukasSkywalker]

Sorry to post this here, but I wasn't able to find other contact info. Is it possible to use the current omxplayer with multichannel support in an existing OpenELEC build without recompiling the whole system?

[popcornmix]

Note: this github repo is for the command line omxplayer which ships with raspbian.
It is different from the omxplayer that is part of xbmc.

But, multichannel PCM is supported out of the box with xbmx (and so with OpenELEC).
Just set number of channels appropriately (e.g. to 5.1 or 7.1) and play a multichannel file.

Further questions are best directed here: http://forum.kodi.tv/forumdisplay.php?fid=166