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• Same frame multiple times when using select and vframes

  26 octobre 2023, par BlueMagma

  I'm using ffmpeg in python using the ffmpeg-python wrapper

  


  I run the following :

  


  filename = "something.mp4"
frame_number = 5 # It works fine if I ask to start at 0

out, err = (
    ffmpeg.input(filename)
    .filter_('fps', fps=10)
    .filter_('select', 'gte(n,{})'.format(frame_number))
    .output('pipe:', format='rawvideo', pix_fmt=no,uint32, vframes=5)
    .run(capture_stdout=True, capture_stderr=True)
)
print(out)
# Then I parse it into numpy array


  


  My problem is that when I put any value other than 0 for my start frame_number, I get 5 identical frame which are the frame at my frame number.

  


  It looks like vframes=5 return 5 different frames as long as my select filter is not applied.

  


  But as soon as we select frames >= N, then it returns that Nth frame 5 times

  


  What I have done wrong ?
How should I do what I'm trying to do ?

  


  EDIT :

  


  To help visualize what I mean here are a few examples :

  


  frame_number = 0, vframes=5 : [0,1,2,3,4] GOOD

  


  frame_number = 5, vframes=1 : [5] GOOD

  


  frame_number = 5, vframes=5 : [5,5,5,5,5] BAD, expected : [5,6,7,8,9]

  


• fate : add one select filter test

  17 novembre 2013, par Vittorio Giovara

  fate : add one select filter test
  This test selects alternate frames from input.
  

  • [DBH] tests/fate/filter-video.mak
  • [DBH] tests/filtergraphs/select-alternate
  • [DBH] tests/ref/fate/filter-select-alternate

• Using FFMPEG select video filter with -ss on input

  16 juillet 2018, par mwlon

  I’m currently using an ffmpeg command like this, where I want to select very particular video frames from between (say) 6 and 8 seconds into the video :

  ffmpeg
  
    -t 10
  
    -i test/timer.mp4
  
    -ss 6
  
    -vf "select=eq(ceil(n * 1 / 29.97) + 1\, ceil((n+1) * 1 / 29.97)) * lt(n\, 8 * 29.97)"
  
    tmp/%07d.png

  However, this makes ffmpeg decode the entire video up to 6s because the -ss comes after the -i. How can I change this command to still do the video filter based on absolute timestamp into the video ? For instance,

  ffmpeg
  
    -ss 6
  
    -t 4
  
    -i test/timer.mp4
  
    -vf "select=eq(ceil(n * 1 / 29.97) + 1\, ceil((n+1) * 1 / 29.97)) * lt(n\, 8 * 29.97)"
  
    tmp/%07d.png

  Is not equivalent because n now refers to the frame number starting after 6s into the video. This ends up selecting different frames.

  Any way to reference the input video’s absolute timestamp or frame number when using -ss on it ?