put_le32(pb, pos - start);
put_le32(pb, (UINT32)(pos - start));
void end_tag(ByteIOContext *pb, offset_t start){    offset_t pos;    pos = url_ftell(pb);    url_fseek(pb, start - 4, SEEK_SET);    put_le32(pb, pos - start);    url_fseek(pb, pos, SEEK_SET);}