lavf/utils: Respect default disposition when select the AVStream

Respect default disposition when select the AVStream
Signed-off-by: Jun Zhao <barryjzhao@tencent.com>

libavformat/utils.c

@@ -4218,7 +4218,8 @@ int av_find_best_stream(AVFormatContext *ic, enum AVMediaType type,
                 continue;
             }
         }
-        disposition = !(st->disposition & (AV_DISPOSITION_HEARING_IMPAIRED | AV_DISPOSITION_VISUAL_IMPAIRED));
+        disposition = !(st->disposition & (AV_DISPOSITION_HEARING_IMPAIRED | AV_DISPOSITION_VISUAL_IMPAIRED))
+                      + !! (st->disposition & AV_DISPOSITION_DEFAULT);
         count = st->codec_info_nb_frames;
         bitrate = par->bit_rate;
         multiframe = FFMIN(5, count);