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[regulararmy <question661623@xxxxxxxxxxxxxxxxxxxxx>]

Question #661623 on rohc changed:
https://answers.launchpad.net/rohc/+question/661623

regulararmy posted a new comment:
I  modify the code in the RTP callback,it shows as follows:
uint8_t count = 0;
uint32_t ssrc[4] = {0};
static bool rtp_detect_cb(const unsigned char *const ip,
                          const unsigned char *const udp,
                          const unsigned char *const payload,
                          const unsigned int payload_size,
                          void *const rtp_private)
{
	const uint16_t max_well_known_port = 1024;
	const uint16_t sip_port = 5060;
	uint16_t udp_sport;
	uint16_t udp_dport;
	uint16_t udp_len;
	uint8_t rtp_pt;
	uint32_t currentSsrc ;
	bool is_rtp = false;

	assert(ip != NULL);
	assert(udp != NULL);
	assert(payload != NULL);
	assert(rtp_private == NULL);

	/* retrieve UDP source and destination ports and UDP length */
	memcpy(&udp_sport, udp, sizeof(uint16_t));
	memcpy(&udp_dport, udp + 2, sizeof(uint16_t));
	memcpy(&udp_len, udp + 4, sizeof(uint16_t));

	/* RTP streams do not use well known ports */
	if(ntohs(udp_sport) <= max_well_known_port ||
	   ntohs(udp_dport) <= max_well_known_port)
	{
		goto not_rtp;
	}

	/* SIP (UDP/5060) is not RTP */
	if(ntohs(udp_sport) == sip_port && ntohs(udp_dport) == sip_port)
	{
		goto not_rtp;
	}

	/* the UDP destination port of RTP packet is even (the RTCP destination
	 * port are RTP destination port + 1, so it is odd) */
	if((ntohs(udp_dport) % 2) != 0)
	{
		goto not_rtp;
	}

	/* UDP Length shall not be too large */
	if(ntohs(udp_len) > 200)
	{
		goto not_rtp;
	}

	/* UDP payload shall at least contain the smallest RTP header */
	if(payload_size < 12)
	{
		goto not_rtp;
	}

	/* RTP version bits shall be 2 */
	if(((payload[0] >> 6) & 0x3) != 0x2)
	{
		goto not_rtp;
	}

	/* RTP payload type shall be GSM (0x03), ITU-T G.723 (0x04),
	 * ITU-T G.729 (0x12), dynamic RTP type 97 (0x61),
	 * telephony-event (0x65), Speex (0x72),
	 * or dynamic RTP type 125 (0x7d) */
	rtp_pt = payload[1] & 0x7f;
	if(rtp_pt != 0x03 && rtp_pt != 0x04 && rtp_pt != 0x12 && rtp_pt != 0x61 &&
	   rtp_pt != 0x65 && rtp_pt != 0x72 && rtp_pt != 0x7d)
	{
		goto not_rtp;
	}

    memcpy(&currentSsrc, payload + 8, sizeof(uint32_t));
    if(ssrc[0] != ntohl(currentSsrc) || ssrc[1] != ntohl(currentSsrc)||ssrc[2] != ntohl(currentSsrc) || ssrc[3] != ntohl(currentSsrc))
    {
        ssrc[count++ & 0x03] = ntohl(currentSsrc);
        goto not_rtp;
    }
	/* we think that the UDP packet is a RTP packet */
	is_rtp = true;

not_rtp:
	return is_rtp;
}

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