lavr: fix mixing matrix reduction when normalization is disabled

In some cases when an input contributes fully to the corresponding
output, other inputs may also contribute to the same output. This is the
case, for example, for the default 5.1 to stereo downmix matrix without
normalization.

diff --git a/libavresample/audio_mix.c b/libavresample/audio_mix.c
index 487bddf7465240b717b8979331d50fd928ce680c..b69bfbcf3edcc4f80b31a3da087d90b4a76660a4 100644 (file)
--- a/libavresample/audio_mix.c
+++ b/libavresample/audio_mix.c
@@ -572,11 +572,22 @@ static void reduce_matrix(AudioMix *am, const double *matrix, int stride)
         int skip = 1;
 
         for (o = 0; o < am->out_channels; o++) {
+            int i0;
             if ((o != i && matrix[o * stride + i] != 0.0) ||
                 (o == i && matrix[o * stride + i] != 1.0)) {
                 skip = 0;
                 break;
             }
+            /* if the input contributes fully to the output, also check that no
+               other inputs contribute to this output */
+            if (o == i) {
+                for (i0 = 0; i0 < am->in_channels; i0++) {
+                    if (i0 != i && matrix[o * stride + i0] != 0.0) {
+                        skip = 0;
+                        break;
+                    }
+                }
+            }
         }
         if (skip) {
             am->input_skip[i] = 1;