rtp: use uint64_t for ts_arrive and fix video jitter calculation

include/re_rtp.h

@@ -23,7 +23,7 @@ struct rtp_header {
 	uint8_t  pt;        /**< Payload type           */
 	uint16_t seq;       /**< Sequence number        */
 	uint32_t ts;        /**< Timestamp              */
-	uint32_t ts_arrive; /**< Arrival Timestamp      */
+	uint64_t ts_arrive; /**< Arrival Timestamp      */
 	uint32_t ssrc;      /**< Synchronization source */
 	uint32_t csrc[16];  /**< Contributing sources   */
 	struct {

src/rtp/rtcp.h

@@ -44,6 +44,7 @@ struct rtp_source {
 	uint64_t sr_recv;         /**< When the last SR was received       */
 	struct ntp_time last_sr;  /**< NTP Timestamp from last SR received */
 	uint32_t rtp_ts;          /**< RTP timestamp                       */
+	uint32_t last_rtp_ts;     /**< Last RTP timestamp                  */
 	uint32_t psent;           /**< RTP packets sent                    */
 	uint32_t osent;           /**< RTP octets sent                     */
 };

src/rtp/sess.c

@@ -598,12 +598,19 @@ void rtcp_sess_rx_rtp(struct rtcp_sess *sess, struct rtp_header *hdr,
 
 	if (sess->srate_rx) {
 		/* Convert from wall-clock time to timestamp units */
-		hdr->ts_arrive =
-			(uint32_t)(tmr_jiffies() * sess->srate_rx / 1000);
-
-		source_calc_jitter(mbr->s, hdr->ts, hdr->ts_arrive);
+		hdr->ts_arrive = tmr_jiffies() * sess->srate_rx / 1000;
+
+		/*
+		 * Calculate jitter only when the timestamp is different than
+		 * last packet (see RTP FAQ
+		 * https://www.cs.columbia.edu/~hgs/rtp/faq.html#jitter).
+		 */
+		if (hdr->ts != mbr->s->last_rtp_ts)
+			source_calc_jitter(mbr->s, hdr->ts,
+					   (uint32_t)hdr->ts_arrive);
 	}
 
+	mbr->s->last_rtp_ts = hdr->ts;
 	mbr->s->rtp_rx_bytes += payload_size;
 }