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• How to know the delay of frames between 2 videos, to sync an audio from video 1 to video 2 ?

  8 janvier 2021, par jaimepm

  world.

  


  I have many videos that I want to compare one-to-one to check if they are the same, and get from there the delay of frames, let's say. What I do now is opening both video files with virtualdub and checking manually at the beginning of video 1 that a given frame is at position, i.e., 4325. Then I check video 2 to see the position of the same frame, i.e., 5500. That would make a delay of +1175 frames. Then I check at the end of the video 1 another given frame, position let's say 183038. I check too the video 2 (imagine the position is 184213) and I calculate the difference, again +1175 : eureka, same video !
The frame I chose to compare aren't exactly random, it must be one that I know it is exactly one I can compare to (for example, a scene change, an explosion that appears from one frame to another, a dark frame after a lighten one...) and I always try to check for the first comparison frames within the first 10000 positions and for the second check I take at the end.
What I do next is to convert the audio from video 1 to video 2 calculating the number of ms needed, but I don't need help with that. I'd love to automatize the comparison so I just have to select video 1 and video 2, nothing else, that way I could forget forever virtualdub and save a lot of time.

  


  I'm tagging this post as powershell too because I'm making a script where at the moment I have to introduce the delay between frames (after comparing manually) myself. It would be perfect that I could add this at the beginning of the script.

  


  Thanks !

  


• ffmpeg mkv to mp4 conversion has color tint

  25 novembre 2020, par razvan

  I am recording the screen in a lossless format to have small CPU load

  


  ffmpeg -f gdigrab -framerate 30 -i desktop -vcodec libx264rgb -crf 0 -preset ultrafast rec.mkv
  
ffprobe rec.mkv

  


  Input #0, matroska,webm, from 'vid.mkv':
  Metadata:
    ENCODER         : Lavf58.64.100
  Duration: 00:00:29.67, start: 0.000000, bitrate: 2829 kb/s
    Stream #0:0: Video: h264 (High 4:4:4 Predictive), gbrp(pc, gbr/unknown/unknown, progressive), 1920x1200, 30 fps, 30 tbr, 1k tbn, 60 tbc (default)
    Metadata:
      ENCODER         : Lavc58.112.103 libx264rgb
      DURATION        : 00:00:29.666000000


  


  then I convert/compress it in mp4

  


  ffmpeg -i rec.mkv rec.mp4
  
ffprobe rec.mp4

  


  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'vid.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    encoder         : Lavf58.64.100
  Duration: 00:00:29.67, start: 0.000000, bitrate: 326 kb/s
    Stream #0:0(und): Video: h264 (High 4:4:4 Predictive) (avc1 / 0x31637661), gbrp(tv, gbr/unknown/unknown), 1920x1200, 248 kb/s, 30 fps, 30 tbr, 15360 tbn, 60 tbc (default)


  


  but the resulting mp4 it is tinted by green and pink color (white areas are tinted green and dark areas are tinted pink)

  


  I have the same results on windows and ubuntu.
I am using latest git versions.

  


  Any idea how to properly convert this to mp4 ?

  


• Remove frames based off an image with FFmpeg

  15 novembre 2020, par VEXED

  The Goal : Take a frame or a reference image and use that to decide what frames to keep/remove from an old screen recording (no audio).

  


  To be slightly more specific, I want to match a specific program that is being used in the screen recording. The program is always full screen and could potentially be identified just by a crop of the top left corner.

  


  The Question : What would be the best way to take an image, in particular a cropped corner of say 100px width and height, and look for the same matching corner in a video ? I would want to output those matches to a new file, that or remove the non-matching frames and create a new file with all the frames that match.

  


  What I Know : I know that duplicate frame removal is very possible, and I already use that for screen recordings.

  


  -filter:v mpdecimate, setpts=N/FRAME_RATE/TB \


  


  The above is being used in my screen recording script to remove duplicate frames.

  


  I'm also aware that you can crop using FFmpeg, but I'm not looking to have actual cropped output. I'm only looking to use a crop to find the portion that matches my reference image or reference frame.

  


  ffmpeg -i in.mp4 -filter:v "crop=out_w:out_h:x:y" out.mp4


  


  The above is a basic crop.

  


  The only reference to finding frames by images is this one. It didn't do what I wanted and just produced dark and distorted output. Though I might be understanding what the aim of that post was incorrectly.

  


  Notes : Thanks in advance for any help, this frame/image matching doesn't have to be done while recording, but can be done in post.