ffmpeg: add a grow_array() helper function

Originally committed as revision 25297 to svn://svn.ffmpeg.org/ffmpeg/trunk

ffmpeg.c

@@ -647,6 +647,26 @@ static int ffmpeg_exit(int ret)
     return ret;
 }
 
+/* similar to ff_dynarray_add() and av_fast_realloc() */
+static void *grow_array(void *array, int elem_size, int *size, int new_size)
+{
+    if (new_size >= INT_MAX / elem_size) {
+        fprintf(stderr, "Array too big.\n");
+        ffmpeg_exit(1);
+    }
+    if (*size < new_size) {
+        uint8_t *tmp = av_realloc(array, new_size*elem_size);
+        if (!tmp) {
+            fprintf(stderr, "Could not alloc buffer.\n");
+            ffmpeg_exit(1);
+        }
+        memset(tmp + *size*elem_size, 0, (new_size-*size) * elem_size);
+        *size = new_size;
+        return tmp;
+    }
+    return array;
+}
+
 static void choose_sample_fmt(AVStream *st, AVCodec *codec)
 {
     if(codec && codec->sample_fmts){