avformat/mov: use rfps_add_frame() only for video

it makes no sense for other streams
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/mov.c

@@ -2159,7 +2159,7 @@ static void mov_build_index(MOVContext *mov, AVStream *st)
                     av_dlog(mov->fc, "AVIndex stream %d, sample %d, offset %"PRIx64", dts %"PRId64", "
                             "size %d, distance %d, keyframe %d\n", st->index, current_sample,
                             current_offset, current_dts, sample_size, distance, keyframe);
-                    if (st->nb_index_entries < 100)
+                    if (st->codec->codec_type == AVMEDIA_TYPE_VIDEO && st->nb_index_entries < 100)
                         ff_rfps_add_frame(mov->fc, st, current_dts);
                 }