avformat/mov.c: require tfhd to begin parsing trun

Detecting missing tfhd avoids re-using tfhd track info from the previous
moof. For files with multiple tracks, this may make a mess of the
avindex and fragindex, which can later trigger av_assert0 in
mov_read_trun().
Reviewed-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavformat/isom.h

@@ -87,6 +87,7 @@ typedef struct MOVAtom {
 struct MOVParseTableEntry;
 
 typedef struct MOVFragment {
+    int found_tfhd;
     unsigned track_id;
     uint64_t base_data_offset;
     uint64_t moof_offset;

libavformat/mov.c

@@ -1366,6 +1366,9 @@ static void fix_frag_index_entries(MOVFragmentIndex *frag_index, int index,
 
 static int mov_read_moof(MOVContext *c, AVIOContext *pb, MOVAtom atom)
 {
+    // Set by mov_read_tfhd(). mov_read_trun() will reject files missing tfhd.
+    c->fragment.found_tfhd = 0;
+
     if (!c->has_looked_for_mfra && c->use_mfra_for > 0) {
         c->has_looked_for_mfra = 1;
         if (pb->seekable & AVIO_SEEKABLE_NORMAL) {
@@ -4544,6 +4547,8 @@ static int mov_read_tfhd(MOVContext *c, AVIOContext *pb, MOVAtom atom)
     MOVTrackExt *trex = NULL;
     int flags, track_id, i;
 
+    c->fragment.found_tfhd = 1;
+
     avio_r8(pb); /* version */
     flags = avio_rb24(pb);
 
@@ -4679,6 +4684,11 @@ static int mov_read_trun(MOVContext *c, AVIOContext *pb, MOVAtom atom)
     AVIndexEntry *new_entries;
     MOVFragmentStreamInfo * frag_stream_info;
 
+    if (!frag->found_tfhd) {
+        av_log(c->fc, AV_LOG_ERROR, "trun track id unknown, no tfhd was found\n");
+        return AVERROR_INVALIDDATA;
+    }
+
     for (i = 0; i < c->fc->nb_streams; i++) {
         if (c->fc->streams[i]->id == frag->track_id) {
             st = c->fc->streams[i];