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• Detect video frame offset to sync videos the smart way

  29 août 2018, par Fabien Biller

  When recording video, we know that it has for instance 60 fps. But do we also know, what the video offset is ? We do know that the time difference between frames is 1/60 s. But when did it start as an absolute value ? The problem comes into play when trying to sync two videos of the same scenery, for instance stereo with different cameras that were not frame-locked. My idea is to interpolate two - audio synced - 60 fps videos to for instance 180 fps to then change them to 60 fps again to hopefully have matching frames. This does not work, according to my test. A better solution would be to know the time difference between frames to interpolate based on difference, for instance using a deep learning algorithm.

  How can ffmpeg help me here ?

• Concatenate multiple videos with a black screen loop into one video

  21 mars 2016, par AHC

  I am using ffmpeg to join a bunch of videos together.
  I am using the classic join ffmpeg code :
  

  ffmpeg -f concat -i joinlist.txt -c copy joinedfile.mp4

  but the problem is that the videos are of different formats, encodings, but the same size : all 640x480. I want to join them all and put a black screen video with no sound every other video :

  video1 + black_screen_video + video2 + black_screen_video + video3 ...

  I generated a black screen video of 2 seconds duration using :

  ffmpeg -f lavfi -i color=c=black:s=640x480:d=2 black_screen_video.mp4

  so all of the videos are of the same size : 640x480, and 25 fps but different codecs. The videos have sound, except for the black screen video.
  I can’t do anything manual, because the number of videos are around several hundred. So it has got to be an automatic way to do all this.

  When I joined them together using the above code, the resulting video does not play correctly at all.

  I know that I have to re-encode them, but how to do this to all these videos at once, with one line of code ?

  Update :
  I am already using with success this code to join them together, but only three, if I have more than one hundred, it is time consuming to write down one by one :

  ffmpeg -i vid1.avi -i vid2.avi -i vid3.avi -filter_complex "[0:v:0] [0:a:0] [1:v:0] [1:a:0] [2:v:0] [2:a:0] concat=n=3:v=1:a=1 [v] [a]" -map "[v]" -map "[a]" output.mp4

  but this is joining only the videos, not looping the black screen video. When I do with black screen, ffmpeg gives me stream matching errors.

  update :

  here is the console image :
  

  2nd update :

  a very long list of errors in red, of which a screenshot here :
  

• ffmpeg combine multiple FHD videos with concat option, but output is HD

  9 mars 2021, par Zawazawa

  I'm trying to combine multiple 1920x1080 videos(.MTS) with concat option, but output resolution is 1280x720.

  


  How can I combine multiple videos with keeping resolution ?

  


  Script is below.

  


  ffmpeg -safe 0 -f concat -i content_dir.txt -c:v copy -c:a copy -map 0:v -map 0:a output.MTS

  


  and the content of input text is below

  


  file '1.MTS'
file '2.MTS'
file '3.MTS'
file '4.MTS'


  


  the information of source videos is below.

  


  video codec h264_nvenc
audio codec ac3


  


  the output of command prompt is below.

  


  Input #0, concat, from 'E:\VideoMaker3\tmp_videos_o3_1\content_dir.txt':
  Duration: N/A, start: 0.000000, bitrate: 192 kb/s
    Stream #0:0: Video: h264 (Main) ([27][0][0][0] / 0x001B), yuv420p(progressive), 1280x720 [SAR 1:1 DAR 16:9], 15 fps, 15 tbr, 90k tbn, 30 tbc
    Stream #0:1(eng): Audio: ac3 ([129][0][0][0] / 0x0081), 48000 Hz, stereo, fltp, 192 kb/s


  


  Thank you.

  


  Add

  


  This problem was caused by a little mistake. One of the input videos was 1280x720, so the resolution of the output was not FHD.
Thank you guys who gave me a comment.