MPEG2/TS获取PCR PID方法

一个简单的从指定MPEG2/TS文件中获取PCR PID的函数，

PMT的头结构中有PCR PID,我们首先得到PMT PID，然后分析PMT包，就可以得到PCR PID了。

GetPmtPid函数的实现见：http://blog.csdn.net/myaccella/article/details/6982596

MAKE_PID:

#define MAKE_PID(p) (((p[0]<<8) + p[1]) & 0x1fff)

 

ushort GetPcrPid(const char* filename)
{
#define TSPACKET_SIZE     188 
	ushort pid, pmtpid, pcrpid = 0;
	uchar buf[TSPACKET_SIZE];
	uchar* p = buf;
	FILE*  fp;
	
	pmtpid = GetPmtPid(filename);
	if (pmtpid == 0) {
		fprintf(stderr, "Unable to get PMT PID!\n");
		return 0;
	}

	fp = fopen(filename, "rb");
	if (fp == NULL) {
		fprintf(stderr, "Failed to open the file %s: %s\n", filename, strerror(errno));
		return 0;
	}


	while (fread(buf, 1, TSPACKET_SIZE, fp) == TSPACKET_SIZE) {
		if (buf[0] != MPEG_TS_SYNC_BYTE) { // @MPEG_TS_SYNC_BYTE = 0x47
			fprintf(stderr, "No sync byte!\n");
			break;
		}

		p = buf;
		pid = MAKE_PID((p+1));
		if( pid != pmtpid ) {
			// Not a  PMT packet
			continue;
		}

		// payload_unit_start_indicator 必须为1
		if (!(buf[1] >> 6 & 0x01)) {
			fprintf(stderr, "No payload_unit_start_indicator!\n");
			continue;
		}

		// Skip the TS header
		p += MPEG_TS_HEADER_SIZE; //@MPEG_TS_HEADER_SIZE = 4

		// Adaptation field exist or not
		if ((buf[3] >> 4 & 0x03) & 0x2) {
			fprintf(stderr, "Adaptation field exist\n");
			p += 1 + p[0];  // p[0]是Adaptation field长度, 1为长度域
		}

		// p[0] 为 Point field长度， 1为Point field
		p += 1 + p[0];

		// 8 为PCR PID在PMT表头中的偏移
		p += 8;

		// 取到的PCR PID如果是0x1fff, 则需要继续取
		pcrpid = MAKE_PID(p);
		if (pcrpid == 0x1fff) {
			pcrpid = 0;
			continue;
		}
		
		break;
	}
         fclose(fp);
	return pcrpid;
}