albm 3gp tag has optional track field not date

Originally committed as revision 23267 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/movenc.c

@@ -1530,7 +1530,7 @@ static int mov_write_3gp_udta_tag(ByteIOContext *pb, AVFormatContext *s,
         put_be16(pb, language_code("eng")); /* language */
         put_buffer(pb, t->value, strlen(t->value)+1); /* UTF8 string value */
         if (!strcmp(tag, "albm") &&
-            (t = av_metadata_get(s->metadata, "date", NULL, 0)))
+            (t = av_metadata_get(s->metadata, "track", NULL, 0)))
             put_byte(pb, atoi(t->value));
     }
     return updateSize(pb, pos);