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• Why is the resulting clip of my ffmpeg concatenation much longer than expected ?

  21 mai 2018, par joeycato

  I’d like to extract a set of clips from a 60fps input video, change each of their durations, then recombine those modified clips. Unfortunately when I attempt this, the resulting clip doesn’t exactly match the sum of those durations.

  Here’s my repro case :

  1. Extend an extracted 2-second clip to 4 seconds ( input frame count = 120 = 60fps * 2 sec ) )

  ffmpeg -y -ss 8 -t 2 -i ./clip_60fps.avi -filter:v "settb=(4/120),setpts=(4/120)*N/TB" -r 120/4 -vcodec huffyuv step1.avi

  2. Shorten an extracted 4-second clip to 1 second ( input frame count = 240 = 60fps * 4 sec )

  ffmpeg -y -ss 10 -t 4 -i ./clip_60fps.avi -filter:v "settb=(1/240),setpts=(1/240)*N/TB" -r 240/1 -vcodec huffyuv step2.avi

  3. Concatenate the modified clips :

  mylist.txt contents :

  file './step1.avi'
  
  file './step2.avi'

  ffmpeg -y -safe 0 -f concat -i ./mylist.txt -r 60 -vcodec huffyuv steps_joined.avi

  The result :

  ffmpeg -i step1.avi 2>&1 | grep Duration
  
  ffmpeg -i step2.avi 2>&1 | grep Duration
  
  ffmpeg -i steps_joined.avi 2>&1 | grep Duration

  Duration : 00:00:04.00, start : 0.000000, bitrate : 3228 kb/s

  Duration : 00:00:01.00, start : 0.000000, bitrate : 23132 kb/s

  Duration : 00:00 :39.98, start : 0.000000, bitrate : 910 kb/s

  Why am I not getting an exact result of 5 seconds, but instead a much larger value ?

• FFMPEG - 2-pass video conversion final file size is larger than expected

  14 juin 2022, par Kevin Korb

  We are converting files and the target filesize is important. For one version of the video it can not be above 750KB.

  


  We are using the 2-pass encoding and specifying the target audio bitrate and target video bitrate, however the longer the duration of the video, the larger the file becomes and exceeds our 750KB target.

  


  


  For example, our file is 53.3 seconds, we know our final target of
750KB. We like our audio at 48kbps (mono).

  


  So we calculate our target (total) bitrate at : 750*8/53.3 = 112.57
total kbps Audio bitrate = 48kbps Video bitrate = 112-48 = 64kbps
video

  


  We would expect the file produced to be 746.2KB. (112*53.3 / 8)

  


  The file produced is 850k(ish).

  


  


  Is there something that takes up space in the file that isn't video or audio that we need to take into consideration ?

  


• MoviePy swaps the height and width of the video

  29 février 2024, par Martin Tošner

  I am trying to work with MoviePy, but every time I work with a video whose height is greater than its width, MoviePy swaps the height and width of the video, as you can see in the picture. 1
Does anyone have any idea how to solve this please ?

  


  def compress_video(old_video_filename, new_video_filename):
    video = VideoFileClip(str(UPLOAD_FOLDER) + str(old_video_filename))
    video.write_videofile(str(UPLOAD_FOLDER) + str(new_video_filename))