avformat/mov: only force parsing for video tracks if stss is empty

Fixes playback of some AAC streams, which are otherwise mangled by the
parser, and stss is typically only valid for video anyway.

Fixes a regression since e41ea866.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 019247bdc3)

libavformat/mov.c

@@ -1679,7 +1679,7 @@ static int mov_read_stss(MOVContext *c, AVIOContext *pb, MOVAtom atom)
     if (!entries)
     {
         sc->keyframe_absent = 1;
-        if (!st->need_parsing)
+        if (!st->need_parsing && st->codec->codec_type == AVMEDIA_TYPE_VIDEO)
             st->need_parsing = AVSTREAM_PARSE_HEADERS;
         return 0;
     }