buf--;
buf++;
int mpegts_parse_packet(MpegTSContext *ts, AVPacket *pkt,                        const uint8_t *buf, int len){    int len1;    len1 = len;    ts->pkt = pkt;    ts->stop_parse = 0;    for(;;) {        if (ts->stop_parse)            break;        if (len < TS_PACKET_SIZE)            return -1;        if (buf[0] != 0x47) {            buf--;            len--;        } else {            handle_packet(ts, buf);            buf += TS_PACKET_SIZE;            len -= TS_PACKET_SIZE;        }    }    return len1 - len;}