if (s->first_rtcp_ntp_time == AV_NOPTS_VALUE) s->first_rtcp_ntp_time = s->last_rtcp_ntp_time;
static int rtcp_parse_packet(AVFormatContext *s1, const unsigned char *buf, int len){    RTPContext *s = s1->priv_data;    if (buf[1] != 200)        return -1;    s->last_rtcp_ntp_time = decode_be64(buf + 8);    s->last_rtcp_timestamp = decode_be32(buf + 16);    return 0;}