Linux Pipeline Sample

Sample code shows how to use pipelin on Linux:

    pid_t pid = 0; 
    int pipefd[2];
  
    pipe(pipefd);
    pid = fork();
    if( -1 == pid ){
      std::cerr << "Fork failed;" << std::endl;
    }
    else if( 0 == pid ){
      int ret = 0;
      // Child process, will start ffmpeg to get meta data info
      
      close(pipefd[0]);  // not care about pipe read end.
      dup2(pipefd[1], 1); // redirect the stdout to pipe write end
      dup2(pipefd[1], 2); // redirect the stderr to pipe write end
      
      close(pipefd[1]);
      
      ret = execlp("ffmpeg","ffmpeg", "-i", filePath.c_str() , NULL);
      
      exit(126);
    }else {
      // Parent process    
      char buffer[4096];
      // not care about the pipe write end; 
      // if we do not close it, the child pipe will not close fully.
      close(pipefd[1]);  
      FILE * pipeFile = NULL;
      int shouldPrint = 0;
      
      pipeFile = fdopen( pipefd[0], "r");  // read from pipe read end.
      // Wait a while, another option is to use wait pid
      sleep(1);
    
      while(1)
      {
        char * p1;
        char * p2;
        
        p1 = fgets( buffer, 4096, pipeFile );
        if(p1 == NULL){
          break;
        }
        
        if( shouldPrint == 0){
          p2 = strstr(p1, "Metadata");
          if(p2){
            shouldPrint = 1;
          }
        }
        else{
          p2 = strstr(p1, "Duration");
          if(p2){
            break;
          }
          std::cout << p1;
        }
      }
      
      fclose(pipeFile);
    }
  }