alacenc : perform decorrelation only for stereo samples

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@14904 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavcodec/alacenc.c

@@ -330,7 +330,8 @@ static void write_compressed_frame(AlacEncodeContext *s)
     int i, j;
 
     /* only simple mid/side decorrelation supported as of now */
-    alac_stereo_decorrelation(s);
+    if(s->avctx->channels == 2)
+        alac_stereo_decorrelation(s);
     put_bits(&s->pbctx, 8, s->interlacing_shift);
     put_bits(&s->pbctx, 8, s->interlacing_leftweight);