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• OpenCV : File Size of H.264 encoded videos

  12 mai 2015, par limekiln

  I write a program that creates a video file out of an image sequence using OpenCV. It runs fine and does what it should, but I realized something I can’t explain. My Videowriter looks like this :

  VideoWriter video(name + ".avi", CV_FOURCC(FOURCC[0], FOURCC[1], FOURCC[2], FOURCC[3]), fps, cvSize((int)width, (int)height));
  
  
  
      for (;;)
  
      {
  
          capture >> frame;
  
          if (frame.empty())
  
              break;
  
          if (!frame.data)
  
          {
  
              cerr << "Could not retrieve frame.";
  
              return -1;
  
          }
  
          video << frame;
  
      }

  For compression, I use either "MJPG", "M4S2" (some MPEG-4 codec) or "X264" (a H.264 codec). I’m getting the "fps" value by user input. Everything works fine, but I found that the output file of X264 encoded videos scales with the fps, the higher the fps the smaller the output file. For the other 2 the size remains the same, just the length of the video changes (as I would expect since it should have the same number of frames, just in another amount of time).
  Can anyone explain me why the file size changes using X264 here ?

• animated gif watermark with logo, text and user id using ffmpeg [duplicate]

  2 décembre 2020, par Pythonsguru

  I have a video, want to add a rotating watermark.gif with draw text on video using ffmpeg command I am using following command, I am using following command for .png it is working fine

  


  ffmpeg -i vid1.mp4 -i watermark.png -filter_complex "[0:v][1:v]overlay=10:10,drawtext=fontfile=arial.ttf:text='Hello':fontcolor=white@1.0:fontsize=30:y=90:x=30:'" -c:a copy -movflags +faststart output.mp4

  


  and using .gif it working fine but

  


  ffmpeg -i "vid1.mp4" -ignore_loop 0 -i "logo.gif" -filter_complex "[1:v]scale=60:50,rotate=PI/6:c=black@0:ow=rotw(PI/6):oh=roth(PI/6) [rotate];[0:v][rotate] overlay=5:5:shortest=1," -codec:a copy -y output.mp4

  


  want to add rotating .gif and text on video in single command

  


• Ffmpeg behaving intermittently

  10 mars 2024, par confused

  I'm noticing something weird, for the first time ever today, and I'm not sure what the problem could even possibly be.

  


  I first noticed it while stripping videos with a python script I wrote. Now I realize it is even happen with command line entry.

  


  Some, but not all videos, and some but not all segments within the same video are not stripping correctly. I'm taking numerous 1-2 hour long videos and cutting segments out of it. When I go to look at the video clip afterwards it automatically jumps to 2, 5, 8, 10 seconds into the video and starts playing there. It depends on the video segment as to how far ahead it skips. If I try to get it to go back and play the first part of the video it won't, it just jumps back to the 2-10 second jump ahead spot and plays from there. In further investigating it is stripping the audio off correctly and keep all the first 2-10 seconds of the audio with the video clip, but it is not picking up the first 2-10 seconds of the video. When I go into VLC Media Player and try to go back to the beginning I have a frozen image on the screen until I get to the 'predestined' 2-10 second mark, and then the video will play fine. When I watch the original video, it is okay but when I strip it the new video doesn't pick up the beginning of the video. Finally had to go to VLC media player to figure that part out as it was the only one who even let me play the underlying audio, every other media player wanted to jump ahead and skip the entire first 2-10 seconds altogether.

  


  This is happening with numerous different videos and video segments within the same video. Some segments it will strip fine others it won't.

  


  This occurs either way, python or command line. I just checked and the underlying video plays fine in the regular media player, until I strip the video, then it wants to skip the first 10 seconds.

  


  How might I fix this problem ?