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• Trouble trimming video by frame number with ffmpeg

  8 décembre 2023, par jgore200377

  I want to trim/split a video with ffmpeg using frames. The reason why is because I am using a Shot Transition Detection model which returns a probability of transition for every frame in the video.

  


  Using timestamps to cut the video has yielded bad results as the precision is not 100%.

  


  Ive tried this command which just outputs the entire video which is DEFINITELY not what I want

  


  ffmpeg -i video.mp4 -vf "trim=start_frame=100:end_frame=200,setpts=PTS-STARTPTS" -c:a copy output.mp4


  


  Ive also tried using python bindings with ffmpeg-python

  


  import ffmpeg

input_file = ffmpeg.input('video.mp4')
output_file = ffmpeg.output(input_file.trim(start_frame=1300, end_frame=1500), 'test_output.mp4')
ffmpeg.run(output_file)


  


  This doesnt work either and outputs a video with half of it being still with unpredictable length

  


  ---

  


  Ive visited some other sites but none seem to have this nailed down and it would be much appreciated if someone can answer how to use frames to trim/split a video with ffmpeg.

  


• Non-Monotonous DTS error in current ffmpeg builds causing frame drops, but not on ffmpeg 1.2

  11 avril 2021, par pentinex

  I'm sorry to ask about such a frequently mentioned subject, but I looked through so many threads and I could never figure out what exactly is wrong, so I'm at the end of my wits. Basically, I want to concat a bunch of .ts files using ffmpeg. I use this command line :

  


  ffmpeg -allowed_extensions ALL -fflags +igndts -i chunklist.m3u8 -c copy "output.mkv"

  


  The .m3u8 file contains all the .ts parts. When I do this and it throws Non-Monotonous DTS errors, the result ends up having dropped frames where the DTS errors occur. I have tried multiple approaches :

  


  

  1. As you see above, I added "-fflags +igndts" at one point, though it doesn't help.

  


  2. I experimented with "-fflags +genpts" just out of desperation. Predictably, this made it worse.

  


  3. I tried muxing video and audio separately, to no avail.

  


  


  But weirdly enough, there is one "solution" : when I use ffmpeg 1.2, the resulting video plays smoothly. It doesn't come without issues. The resulting video always reports a frame rate of half of what it should be (14.98 when it should be 29.97). But it plays just like it should. Ideally though, I wouldn't want to use such an old version of ffmpeg, since I'm sure there are things in the background that may go wrong and I'm not even noticing those, so I'd hope I could get these kinds of results on current builds of ffmpeg.

  


  Does anybody have an idea ? I'm kind of losing my mind with this one.

  


• aarch64 : vp8 : Optimize vp8_idct_add_neon for aarch64

  31 janvier 2019, par Martin Storsjö

  aarch64 : vp8 : Optimize vp8_idct_add_neon for aarch64
  The previous version was a pretty exact translation of the arm
  
  version. This version does do some unnecessary arithemetic (it does
  
  more operations on vectors that are only half filled ; it does 4
  
  uaddw and 4 sqxtun instead of 2 of each), but it reduces the overhead
  
  of packing data together (which could be done for free in the arm
  
  version).
  This gives a decent speedup on Cortex A53, a minor speedup on
  
  A72 and a very minor slowdown on Cortex A73.
  Before :        Cortex A53    A72    A73
  
  vp8_idct_add_neon :   79.7   67.5   65.0
  
  After :
  
  vp8_idct_add_neon :   67.7   64.8   66.7
  Signed-off-by : Martin Storsjö <martin@martin.st>
  

  • [DBH] libavcodec/aarch64/vp8dsp_neon.S