aac channel ordering for multi-channel audio

Date: Sun, 28 Sep 2008 20:17:54 +0200
The channel order of aac 5.1 audio is wrong during playback. IIRC, the
internal channels order for this kind of streams is the same as dts: dts
output is reordered according to alsa specs (and ac3 5.1 also works), but
aac is not and - for instance - front center is send to front left.

The audio channels configuration table should be something like this

##  ---------------------
## | Config:  5.1 Ch     |
##  ---- ----------------  -------------- --------------
## | Ch |     AAC/DTS    |      ALSA     |      AC3     |
##  ---- ---------------- --------------- --------------
## | 00 | Center front   | Left front    | Left front   |
## | 01 | Left front     | Right front   | Center       |
## | 02 | Right front    | Left back     | Right front  |
## | 03 | Left back      | Right back    | Left back    |
## | 04 | Right back     | Center        | Right back   |
## | 05 | LFE            | LFE           | LFE          |
##  ---- ---------------- --------------- --------------

1 files changed, 26 insertions, 1 deletions

diff --git a/src/libfaad/xine_faad_decoder.c b/src/libfaad/xine_faad_decoder.c
index ae71af155..9c657610e 100644
--- a/src/libfaad/xine_faad_decoder.c
+++ b/src/libfaad/xine_faad_decoder.c
@@ -275,7 +275,32 @@ static void faad_decode_audio ( faad_decoder_t *this, int end_frame ) {
 
       lprintf("decoded %d/%d output %ld\n",
               used, this->size, this->faac_finfo.samples );
-      
+
+      /* Performing necessary channel reordering because aac uses a different
+       * layout than alsa:
+       *
+       *  aac 5.1 channel layout: c l r ls rs lfe
+       * alsa 5.1 channel layout: l r ls rs c lfe
+       *
+       * Reordering is only necessary for 5.0 and above. Currently only 5.0
+       * and 5.1 is being taken care of, the rest will stay in the wrong order
+       * for now.
+       *
+       * WARNING: the following needs a output format of 16 bits per sample.
+       *    TODO: - reorder while copying (in the while() loop) and optimizing
+       */
+      if(this->num_channels == 5 || this->num_channels == 6)
+      {
+        int i         = 0;
+        uint16_t* buf = (uint16_t*)(sample_buffer);
+
+        for(; i < this->faac_finfo.samples; i += this->num_channels) {
+          uint16_t center         = buf[i];
+          *((uint64_t*)(buf + i)) = *((uint64_t*)(buf + i + 1));
+          buf[i + 4]              = center;
+        }
+      }
+
       while( decoded ) {
         audio_buffer = this->stream->audio_out->get_buffer (this->stream->audio_out);