int mov_write_mdat_tag(ByteIOContext *pb, MOVTrack* track)
int mov_write_mdat_tag(ByteIOContext *pb, MOVContext* mov)
int mov_write_mdat_tag(ByteIOContext *pb, MOVTrack* track){    track->mdat_pos = url_ftell(pb);     put_be32(pb, 0); /* size placeholder*/    put_tag(pb, "mdat");    return 0;}