avcodec/aacdec: warn user when remapping streams.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/aac.h

@@ -274,6 +274,7 @@ struct AACContext {
     ChannelElement          *che[4][MAX_ELEM_ID];
     ChannelElement  *tag_che_map[4][MAX_ELEM_ID];
     int tags_mapped;
+    int warned_remapping_once;
     /** @} */
 
     /**

libavcodec/aacdec.c

@@ -621,6 +621,12 @@ static ChannelElement *get_che(AACContext *ac, int type, int elem_id)
          * If we seem to have encountered such a stream, transfer
          * the LFE[0] element to the SCE[1]'s mapping */
         if (ac->tags_mapped == tags_per_config[ac->oc[1].m4ac.chan_config] - 1 && (type == TYPE_LFE || type == TYPE_SCE)) {
+            if (!ac->warned_remapping_once && (type != TYPE_LFE || elem_id != 0)) {
+                av_log(ac->avctx, AV_LOG_WARNING,
+                   "This stream seems to incorrectly report its last channel as %s[%d], mapping to LFE[0]\n",
+                   type == TYPE_SCE ? "SCE" : "LFE", elem_id);
+                ac->warned_remapping_once++;
+            }
             ac->tags_mapped++;
             return ac->tag_che_map[type][elem_id] = ac->che[TYPE_LFE][0];
         }
@@ -637,6 +643,12 @@ static ChannelElement *get_che(AACContext *ac, int type, int elem_id)
          * If we seem to have encountered such a stream, transfer
          * the SCE[1] element to the LFE[0]'s mapping */
         if (ac->tags_mapped == tags_per_config[ac->oc[1].m4ac.chan_config] - 1 && (type == TYPE_LFE || type == TYPE_SCE)) {
+            if (!ac->warned_remapping_once && (type != TYPE_SCE || elem_id != 1)) {
+                av_log(ac->avctx, AV_LOG_WARNING,
+                   "This stream seems to incorrectly report its last channel as %s[%d], mapping to SCE[1]\n",
+                   type == TYPE_SCE ? "SCE" : "LFE", elem_id);
+                ac->warned_remapping_once++;
+            }
             ac->tags_mapped++;
             return ac->tag_che_map[type][elem_id] = ac->che[TYPE_SCE][1];
         }