[FFmpeg-cvslog] swr: update side to back mixing.

[Justin Ruggles]

ffmpeg | branch: master | Justin Ruggles <justin.ruggles at gmail.com> | Wed May  2 00:16:04 2012 +0200| [9b42653b22d43b89de96a00abe7fd61f9e048eb2] | committer: Michael Niedermayer

swr: update side to back mixing.

Signed-off-by: Michael Niedermayer <michaelni at gmx.at>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=9b42653b22d43b89de96a00abe7fd61f9e048eb2
---

 libswresample/rematrix.c |   11 +++++++++--
 1 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/libswresample/rematrix.c b/libswresample/rematrix.c
index 27c4e1b..7728445 100644
--- a/libswresample/rematrix.c
+++ b/libswresample/rematrix.c
@@ -184,8 +184,15 @@ static int auto_matrix(SwrContext *s)
 
     if(unaccounted & AV_CH_SIDE_LEFT){
         if(s->out_ch_layout & AV_CH_BACK_LEFT){
-            matrix[ BACK_LEFT][ SIDE_LEFT]+= 1.0;
-            matrix[BACK_RIGHT][SIDE_RIGHT]+= 1.0;
+            /* if back channels do not exist in the input, just copy side
+               channels to back channels, otherwise mix side into back */
+            if (s->in_ch_layout & AV_CH_BACK_LEFT) {
+                matrix[BACK_LEFT ][SIDE_LEFT ] += M_SQRT1_2;
+                matrix[BACK_RIGHT][SIDE_RIGHT] += M_SQRT1_2;
+            } else {
+                matrix[BACK_LEFT ][SIDE_LEFT ] += 1.0;
+                matrix[BACK_RIGHT][SIDE_RIGHT] += 1.0;
+            }
         }else if(s->out_ch_layout & AV_CH_BACK_CENTER){
             matrix[BACK_CENTER][ SIDE_LEFT]+= M_SQRT1_2;
             matrix[BACK_CENTER][SIDE_RIGHT]+= M_SQRT1_2;