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;
 }