@@ -559,9 +559,12 @@ static void reduce_matrix(AudioMix *am, const double *matrix, int stride)

         if (zero) {

             am->output_zero[o] = 1;

             am->out_matrix_channels--;

+            if (o < am->in_channels)

+                am->in_matrix_channels--;

         }

     }

-    if (am->out_matrix_channels == 0) {

+    if (am->out_matrix_channels == 0 || am->in_matrix_channels == 0) {

+        am->out_matrix_channels = 0;

         am->in_matrix_channels = 0;

         return;

     }

@@ -683,7 +686,7 @@ int ff_audio_mix_set_matrix(AudioMix *am, const double *matrix, int stride)

                                      am->in_matrix_channels;                \

         for (i = 0, i0 = 0; i < am->in_channels; i++) {                     \

             double v;                                                       \

-            if (am->input_skip[i])                                          \

+            if (am->input_skip[i] || am->output_zero[i])                    \

                 continue;                                                   \

             v = matrix[o * stride + i];                                     \

             am->matrix_## type[o0][i0] = expr;                              \