lavr: make sure that the mix function is reset even if no mixing will be done

If the matrix reduction ends up with no mixing matrix needed, we need to still
reset the mix function accordingly and log the info to the user.

libavresample/audio_mix.c

@@ -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)