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• Windows Pipes STDIN and STDOUT Parent Child proc communication IPC FFMPEG

  15 octobre 2018, par Evren Bingøl

  I am writing a simple WINDOWS app which demonstrates piping,

  I pass byte size data down to child proc, increment the value and send the char size data back to parent and loop until it reaches MAX_CHAR
  Pretty much demonstration of "i++" with IPC.

  Parent Process

  while(i<256){
  
      bSuccess = WriteFile(g_hChildStd_IN_Wr, chBuf, sizeof(char), &dwWritten, NULL);
  
      bSuccess = ReadFile(g_hChildStd_OUT_Rd, chBuf, sizeof(char), &dwRead, NULL); // IF THERE IS NO FFLUSH IT BLOCKS
  
  }

  And in Child

  while (i<256){
  
          byte data=0;
  
          fread(&data, sizeof(char), 1, stdout);
  
          data++;
  
          fwrite(&data, sizeof(char), 1, stdout);
  
          //fflush(stdout); IF I DO NOT HAVE THIS  PARENT BLOCKS ON READ
  
  }

  First of all if I do not FFLUSH child proc stdout, the parent blocks on reading child’s stdout.

  How can one run this code without having to fflush child’s stdout.

  Closing the pipe after child’s first write is not an option as it is in a loop and needs to execute 256 times.

  more generically I want the child to write N bytes to parent, parent read that N bytes do something and write back to child another N bytes and child does something with that N bytes and write to parent N bytes. This happens M times.

  thing is I can not use fflush because my final goal is to use a child process that is not implemented by me.

  My final goal is to pipe data to FFMPEG encode the data and read back from the stdin and do this over and over again with out having to fork a new FFMPEG process for each image frame but rather fork one instance of FFMPEG and pipe data in and read data out from it. And since I did not implement ffmpeg and I can not change the source code.

  thanks

  Thanks

• ffmpeg decode video to YUV and damaged pixels

  28 août 2021, par user3807476

  I use this example to decode a mpeg1 video

  


  when decode starts

  


  log (every 3 to 10 frames) :

  


  [mpeg1video @ 0x5626caf74e40] ac-tex damaged at 39 15
[mpeg1video @ 0x5626caf74e40] Warning MVs not available
[mpeg1video @ 0x5626caf74e40] concealing 405 DC, 405 AC, 405 MV errors in P frame


  


  and the result is :

  


  

  


  I tried make rgb from YUV using opencv but the rgb results is same

  


      cv::Size actual_size(frame->width, frame->height);
    cv::Size half_size(frame->width/2, frame->height/2);
    cv::Mat y(actual_size, CV_8UC1, frame->data[0]);
    cv::Mat u(half_size, CV_8UC1, frame->data[1]);
    cv::Mat v(half_size, CV_8UC1, frame->data[2]);

    cv::Mat u_resized, v_resized;
    cv::resize(u, u_resized, actual_size, 0, 0, cv::INTER_NEAREST); //repeat u values 4 times
    cv::resize(v, v_resized, actual_size, 0, 0, cv::INTER_NEAREST); //repeat v values 4 times

    cv::Mat yuv; 
    std::vector yuv_channels = { y, u_resized, v_resized };
    cv::merge(yuv_channels, yuv);

    cv::Mat bgr;
    cv::cvtColor(yuv, bgr, cv::COLOR_YUV2BGR);
    
    cv::imshow("x",bgr);
    cv::waitKey(1000/25);


  


  

  


• How to split multiple audio files by 10 seconds each on OSX ?

  23 juin 2020, par LA_

  Let's say I have 100 audio files and I would like to split each file into several files with 10 seconds length.

  


  I think the following should work :

  


  for i in *.ogg; do
  echo -n $i ...
  ffmpeg -i $i.ogg -ss 0  -t 10 $i_1.ogg
  ffmpeg -i $i.ogg -ss 10 -t 10 $i_2.ogg
  ffmpeg -i $i.ogg -ss 20 -t 10 $i_3.ogg
done


  


  But I don't understand how many times ffmpeg commands should be repeated.