put_tag(pb, "3gp4");
if (!strcmp("3gp", s->oformat->name)) put_tag(pb, "3gp4"); else put_tag(pb, "mp41");
int mov_write_ftyp_tag(ByteIOContext *pb){    put_be32(pb, 0x14 ); /* size */    put_tag(pb, "ftyp");    put_tag(pb, "3gp4");    put_be32(pb, 0x200 );    put_tag(pb, "3gp4");    return 0x14;}