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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

  


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  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.

  


• Precise seeking with ffmpeg

  6 août 2015, par Taras Galchenko

  Let’s say I have an audio file being decoded with ffmpeg. The source format is something like AAC where the audio is split into packets. When seeking to a particular time, it is clear that the time will not fall, most of the time, on the packet border but somewhere within the packet duration. Do I have to seek within packet myself or av_seek_frame does it all by itself and sets up decoding so that the next decoded frame should start at the position I’ve requested ?

  If I use the function av_seek_frame with the flag AVSEEK_FLAG_BACKWARD, I assume that the next packet returned by av_read_frame will be the packet containing the time position I am seeking to. Is that right ?

  If I decode this packet with avcodec_decode_audio4, will the frame returned contain the audio data at the start time of the packet begining or from the time I’ve passed to av_seek_frame ? In the latter case how can I find out the frame/packet timestamp so as to estimate the number of samples to skip in the decoded frame ? The PTS after seek is zero and DTS looks useless either.

  Is it possible to seek with precision to a particular time using ffmpeg ?

• ffmpeg usb Web cam recording terminates randomly before set duration

  16 mars 2018, par pomptondrive

  The output of this script is just fine ; it’s pretty much what I want. But it seems to terminate randomly. My next step will be to try this on another computer to see if the issue persists.

  My configuration :
  Dell Precision laptop, m4400
  2x Intel(R) Core(TM)2 Duo CPU P8600 @ 2.40GHz
  Linux Mint 18.3 Sylvia
  Kernel : Linux 4.4.0-116-generic (x86_64)
  Card : NVIDIA G96GLM [Quadro FX 770M]
  ffmpeg version 2.8.11-0ubuntu0.16.04.1
  USB Camera-B4.09.24.1 Sony Playstation Eye

  And this is the script that I’m running - the last time it recorded for about three hours and forty-five minutes, before that it was about 55 minutes ; once it ran five and a half hours :

  #!/bin/bash  
  
  echo "This is a shell script to make a timelapse video."  
  
  ffmpeg \
  
  -f v4l2 -input_format yuyv422 -video_size 640x480 -framerate 5 -t 09:00:00 -i /dev/video0 \
  
  -vf "select=not(mod(n\,5)),setpts=N/(60*TB),fps=60, drawtext=fontfile=/usr/share/fonts/truetype/dejavu/DejaVuSansMono.ttf:text='%{localtime\:%T}':x=20:y=20:fontcolor=white" \
  
  -c:v libx264 -preset superfast -crf 23 -pix_fmt yuv422p -g 15 -keyint_min 15 \
  
  -f mpegts /media/dkm/OneTB/Video/Timelapse_$(date +%Y-%m-%d_%H.%M.%S).ts

  Any suggestions would be appreciated. Thanks !