static int rtcp_parse_packet(RTPDemuxContext *s, const unsigned char *buf, int len)
{
    int payload_len;
    while (len >= 2) {
        switch (buf[1]) {
        case RTCP_SR:
            if (len < 16) {
                av_log(NULL, AV_LOG_ERROR, "Invalid length for RTCP SR packet\n");
                return AVERROR_INVALIDDATA;
            }
            payload_len = (AV_RB16(buf + 2) + 1) * 4;

            s->last_rtcp_ntp_time = AV_RB64(buf + 8);
            s->last_rtcp_timestamp = AV_RB32(buf + 16);
            if (s->first_rtcp_ntp_time == AV_NOPTS_VALUE) {
                s->first_rtcp_ntp_time = s->last_rtcp_ntp_time;
                if (!s->base_timestamp)
                    s->base_timestamp = s->last_rtcp_timestamp;
                s->rtcp_ts_offset = s->last_rtcp_timestamp - s->base_timestamp;
            }

            buf += payload_len;
            len -= payload_len;
            break;
        case RTCP_BYE:
            return -RTCP_BYE;
        default:
            return -1;
        }
    }
    return -1;
}