fix d-10 mapping detection

Originally committed as revision 6631 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/mxf.c

@@ -910,7 +910,7 @@ static int mxf_parse_structural_metadata(MXFContext *mxf)
                     st->codec->codec_id = CODEC_ID_PCM_S24BE;
                 else if (descriptor->bits_per_sample == 32)
                     st->codec->codec_id = CODEC_ID_PCM_S32BE;
-                if (descriptor->essence_container_ul[14] == 0x01) /* D-10 Mapping */
+                if (descriptor->essence_container_ul[13] == 0x01) /* D-10 Mapping */
                     st->codec->channels = 8; /* force channels to 8 */
             } else if (st->codec->codec_id == CODEC_ID_MP2) {
                 st->need_parsing = 1;