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• Extract different camera frames (multiplex)

  22 août 2016, par Mike Issa

  I have a sequential multiplexed video with 3 cameras. These videos are being converted from VHS to DVD (.VOB format). I am using ffmpeg to extract all frames in .JPG format.

  I want to write a python script that scans for a certain object in the frame (like a constant/static object in the background) and organizes all the frames containing that object into a folder. This is the only way I can think of to separate the camera views, because as the video progresses, one of the cameras turns off for a few minutes and then turns back on, ruining the interval of 3-frames-per-camera-view sequence*.

  • I tried writing a python script that extracts every third frame (starting from the first frame for camera 1, second frame for camera 2, third frame for camera 3) into separate folders, but this did not bode well when I found out that one of the cameras switches off and then back on.

  I tried a "detection patch" method using VirtualDub found in this forum, but it didn’t work for me (not sure why).

  Should I be using numpy or openCV to find a certain block of pixels in each frame to do the organizing of camera views, or is there a simpler way ?

• 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

• how to put a raw char * to AVPacket

  29 août 2014, par Godspped

  I have a compressed image stored in a char * and I want to put it back to an AVPacket so that I can put it into a ffmpeg decoder. Can someone show how to do this ? Any sample or tutorial would be greatly appreciated.

  Thanks in advance