@@ -527,28 +527,13 @@ int ff_audio_mix_get_matrix(AudioMix *am, double *matrix, int stride)

     return 0;

 }

-int ff_audio_mix_set_matrix(AudioMix *am, const double *matrix, int stride)

+static void reduce_matrix(AudioMix *am, const double *matrix, int stride)

 {

-    int i, o, i0, o0, ret;

-    char in_layout_name[128];

-    char out_layout_name[128];

-

-    if ( am->in_channels <= 0 ||  am->in_channels > AVRESAMPLE_MAX_CHANNELS ||

-        am->out_channels <= 0 || am->out_channels > AVRESAMPLE_MAX_CHANNELS) {

-        av_log(am->avr, AV_LOG_ERROR, "Invalid channel counts\n");

-        return AVERROR(EINVAL);

-    }

-

-    if (am->matrix) {

-        av_free(am->matrix[0]);

-        am->matrix = NULL;

-    }

+    int i, o;

     memset(am->output_zero, 0, sizeof(am->output_zero));

     memset(am->input_skip,  0, sizeof(am->input_skip));

-    memset(am->output_skip, 0, sizeof(am->output_zero));

-    am->in_matrix_channels  = am->in_channels;

-    am->out_matrix_channels = am->out_channels;

+    memset(am->output_skip, 0, sizeof(am->output_skip));

     /* exclude output channels if they can be zeroed instead of mixed */

     for (o = 0; o < am->out_channels; o++) {

@@ -578,7 +563,7 @@ int ff_audio_mix_set_matrix(AudioMix *am, const double *matrix, int stride)

     }

     if (am->out_matrix_channels == 0) {

         am->in_matrix_channels = 0;

-        return 0;

+        return;

     }

     /* skip input channels that contribute fully only to the corresponding

@@ -615,7 +600,7 @@ int ff_audio_mix_set_matrix(AudioMix *am, const double *matrix, int stride)

     }

     if (am->in_matrix_channels == 0) {

         am->out_matrix_channels = 0;

-        return 0;

+        return;

     }

     /* skip output channels that only get full contribution from the

@@ -637,8 +622,31 @@ int ff_audio_mix_set_matrix(AudioMix *am, const double *matrix, int stride)

     }

     if (am->out_matrix_channels == 0) {

         am->in_matrix_channels = 0;

-        return 0;

+        return;

     }

+}

+

+int ff_audio_mix_set_matrix(AudioMix *am, const double *matrix, int stride)

+{

+    int i, o, i0, o0, ret;

+    char in_layout_name[128];

+    char out_layout_name[128];

+

+    if ( am->in_channels <= 0 ||  am->in_channels > AVRESAMPLE_MAX_CHANNELS ||

+        am->out_channels <= 0 || am->out_channels > AVRESAMPLE_MAX_CHANNELS) {

+        av_log(am->avr, AV_LOG_ERROR, "Invalid channel counts\n");

+        return AVERROR(EINVAL);

+    }

+

+    if (am->matrix) {

+        av_free(am->matrix[0]);

+        am->matrix = NULL;

+    }

+

+    am->in_matrix_channels  = am->in_channels;

+    am->out_matrix_channels = am->out_channels;

+

+    reduce_matrix(am, matrix, stride);

 #define CONVERT_MATRIX(type, expr)                                          \

     am->matrix_## type[0] = av_mallocz(am->out_matrix_channels *            \

@@ -664,6 +672,7 @@ int ff_audio_mix_set_matrix(AudioMix *am, const double *matrix, int stride)

     }                                                                       \

     am->matrix = (void **)am->matrix_## type;

+    if (am->in_matrix_channels && am->out_matrix_channels) {

     switch (am->coeff_type) {

     case AV_MIX_COEFF_TYPE_Q8:

         CONVERT_MATRIX(q8, av_clip_int16(lrint(256.0 * v)))

@@ -678,6 +687,7 @@ int ff_audio_mix_set_matrix(AudioMix *am, const double *matrix, int stride)

         av_log(am->avr, AV_LOG_ERROR, "Invalid mix coeff type\n");

         return AVERROR(EINVAL);

     }

+    }

     ret = mix_function_init(am);

     if (ret < 0)