audio_mix: fix zeroing output channels in certain cases
authorAnton Khirnov <anton@khirnov.net>
Mon, 16 Dec 2013 17:44:15 +0000 (18:44 +0100)
committerAnton Khirnov <anton@khirnov.net>
Fri, 3 Jan 2014 15:42:46 +0000 (16:42 +0100)
Specifically, when the corresponding input channel exists and its matrix
column is all-zero (which is necessary for zeroing the output), the
matrix column must be removed from the matrix.

This is not done currently, so the mixing code would end up using
uninitialized pointers from stack.

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
libavresample/audio_mix.c

index 765bc73..211e3c9 100644 (file)
@@ -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;                              \