Recherche avancée

Sur d’autres sites (2511)

• Increase ffmpeg precision for filters like SSIM, PSNR

  3 juin 2021, par Rashiq

  I am trying to calculate the ssim and psnr of an image using ffmpeg ; however, the results are only upto 2 decimal places. Is there a way to increase the precision of the results (higher the better) ?

  


  Output :

  


  n:1 mse_avg:0.00 mse_r:0.00 mse_g:0.00 mse_b:0.00 psnr_avg:76.89 psnr_r:76.88 psnr_g:76.93 psnr_b:76.86


  


  Command used for psnr :

  


  ffmpeg.exe -i original.tiff -i modified.tiff -lavfi psnr=stats_file=psnr_logfile.txt -f null -


  


  Command used for ssim :

  


  ffmpeg.exe -i original.tiff -i modified.tiff -lavfi ssim=stats_file=ssim_logfile.txt -f null -


  


• Is there a faster way to grab frames by skipping frames ?

  18 janvier 2020, par Nick

  Im looping through av_read_frame and avcodec_decode_video2 to read pixel data from an mp4 video.

  int i = 0;
  
  while (av_read_frame(pFormatCtx, &pkt)>=0) {
  
      AVPacket orig_pkt = pkt;
  
      do {
  
          int ret = 0;
  
          int decoded = pkt.size;
  
          got
  
          if (i%7==0) { // Only process 1/7th of frames
  
              ret = avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &pkt);
  
              if (got_frame) {
  
                  // get pixel data
  
              } else {
  
                  printf("Error: could not get frame %d", i );
  
              }
  
          }
  
          ret = decoded;
  
          pkt.data += ret;
  
          pkt.size -= ret;
  
      } while (pkt.size > 0);
  
      av_free_packet(&orig_pkt);
  
  }

  It’s a 35FPS video, but I only need to read about 5FPS of pixel data.

  The i%7==0 conditional results in more than 1/7th of the frames being dropped. Removing that line results in all frames being slowly processed with no frames dropped.

  Is there a fast way to only read 1/7th of the frames ?

• Overlay a video on top of another video at a specific time offset and position using FFmpeg 6 [closed]

  15 janvier 2024, par user1768741

  I have 2 MP4 videos :

  


  

  1. background.mp4 - 720p, 10 seconds long

  


  2. overlay.mp4 - 360p, 3 seconds long

  


  


  I want to create a single video where at first background.mp4 is played, then overlay.mp4 is overlaid on the bottom right corner of background.mp4 (with some padding) starting at 00:00:04 (so both videos are playing simultaneously), then disappearing when it ends (at 00:00:07), while background.mp4 keeps on playing. I want to keep only the audio of background.mp4.

  


  I tried many FFmpeg commands to get this, but I get only partial results :

  


  

  1. Both videos are playing if I start the overlay at 00:00:00

  


  2. Videos are playing but at a very low frame rate (seem to be laggy)

  


  3. Overlay shows only the last frame

  


  


  And more of unwanted results

  


  Also tried OpenCV using Python but to no avail