hust_rtpupdate.c

实现基于ip2022的MPEG2 TS的IP组播接收

/*-------------------------------------------------------------------------
 * rtpupdate.c - rtpupdate, rtpinitseq, rtpupdateseq
 *-------------------------------------------------------------------------
 */

#include "hust_rtp.h"
#include "hust_util.h"
#include "hust_event.h"
#include "hust_linux.h"
#include "hust_hash.h"
///#include <time.h>

#define DEBUG(x) x

/*------------------------------------------------------------------------
 * rtpupdate - update statistics with each RTP packet received. 
 *------------------------------------------------------------------------
 */
int
rtpupdate(struct session *psn, struct stream *pstm, struct rtp *header)
{

	u32_t		now;
	s32_t		delta;
	s32_t		D;

	////if (pthread_mutex_lock(&pstm->stm_mutex) != 0)
	///	return ERROR;

	if (rtpupdateseq(psn, pstm, header->rtp_seq) == ERROR) {
		////pthread_mutex_unlock(&pstm->stm_mutex);
		return ERROR;
	}

	now=timer_get_ticks();


	/*
	 * Check for encoding change.
	 * Post event if detected.
	 */
	if (pstm->stm_payload != header->rtp_payload) {
		pstm->stm_payload = header->rtp_payload;
		rtppostevent(psn, EVENT_PARTICIPANT_ENCODING, pstm->stm_ssrc, NULL, 0);
	}
  ////检查编码(载荷类型payload)的变化，并发出事件通知
	/*
	 * If not first packet, update jitter.
	 */
	if (pstm->stm_packets != 0) {
		if (pstm->stm_clkrt != 0) {
			delta = timeflatten(timesub(now, pstm->stm_lastrec), pstm->stm_clkrt);
			D = delta - (header->rtp_time - pstm->stm_lastts);
			D = (D < 0 ? -D : D);
			pstm->stm_jitter += ((double) D - pstm->stm_jitter) / (double) 16;
		}
	}
	///刷新时间抖动
  
	pstm->stm_packets++;
	pstm->stm_inactive = 0;
	pstm->stm_lastts = header->rtp_time;
	pstm->stm_lastrec = now;
	////pthread_mutex_unlock(&pstm->stm_mutex);
	return OK;
}
////收到一个包后刷新统计信息

/*------------------------------------------------------------------------
 * rtpinitseq - initialize variables related to sequence numbers
 * Adapted from RFC 1889.
 *------------------------------------------------------------------------
 */
void
rtpinitseq(struct stream *pstm, seq_t seq)
{

	pstm->stm_firstseq = seq;
	pstm->stm_hiseq = seq;
	pstm->stm_roll = 0;
	pstm->stm_packets = 0;
	pstm->stm_recprior = 0;
	pstm->stm_expprior = 0;  
}

/*------------------------------------------------------------------------
 * rtpupdateseq - check sequence number of incoming packet and update
 * appropriate counters. Adapted from RFC 1889.
 *------------------------------------------------------------------------
 */
int
rtpupdateseq(struct session *psn, struct stream *pstm, seq_t seq)
////sep是接收到的rtp包的sequence
////pstm是根据接收的rtp包的源标识位查询或创建的stream的指针
{

	seq_t udelta;

	udelta = seq - pstm->stm_hiseq;
////计算接收到的包的序列号与所收到的包的最大的序列号的差
  
	if (pstm->stm_probation) {
		/////如果还在检查期(由stm_probation标识)
		if (seq == pstm->stm_hiseq + 1) {
			////如果收到序列号连续的包
			pstm->stm_probation--;////检查期标识减一
			
			pstm->stm_hiseq = seq;///刷新流中的最高序列号记录
			
			if (pstm->stm_probation == 0) {
				///过了检查期则为这个流初始化queue
				rtpinitseq(pstm, seq);
				return OK;
			}
		} else {
			pstm->stm_probation = RTP_MINSEQUENTIAL - 1;
			pstm->stm_hiseq = seq;
			////连续的包中断，重新设置检查期长度，并把这个包设的序列号
			////设置成队列中最大的
		}
		return ERROR;
	} 
	else if (udelta < RTP_MAXDROPOUT) {
			////限制seq的跳跃不超过RTP_MAXDROPOUT
			if (seq < pstm->stm_hiseq)
				pstm->stm_roll++;
			////表明进入了下一个周期
			pstm->stm_hiseq = seq;
			///刷新stm_hiseq
		}
	else if (udelta <= RTP_SEQMOD - RTP_MAXMISORDER) {
				////如果跳跃太大，要根据stm_badseq来确定是否需要重新
				////初始化队列
				if (seq == pstm->stm_badseq) {
					rtpinitseq(pstm, seq);
					rtppostevent(psn, EVENT_PARTICIPANT_SEQGAP,
						     pstm->stm_ssrc, NULL, 0);
				}
			}
	else {
				pstm->stm_badseq = (seq + 1) & (RTP_SEQMOD - 1);
				////跳跃超出范围，存当前的seq为stm_badseq
				return ERROR;
			}
				
	return OK;
}
////通过seq来确定是否让一个stream度过检查期，并解决序列号前
////后跳跃过大的情况。