MPEG2/TS获取PCR PID方法

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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 = 0x47fprintf(stderr, "No sync byte!\n");break;}p = buf;pid = MAKE_PID((p+1));if( pid != pmtpid ) {// Not a  PMT packetcontinue;}// payload_unit_start_indicator 必须为1if (!(buf[1] >> 6 & 0x01)) {fprintf(stderr, "No payload_unit_start_indicator!\n");continue;}// Skip the TS headerp += MPEG_TS_HEADER_SIZE; //@MPEG_TS_HEADER_SIZE = 4// Adaptation field exist or notif ((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 fieldp += 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;}