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• video distorted after ffmpeg cropping and reencoding [closed]

  27 juillet 2023, par Hemin

  I met an annoying problem when I tried to read frame from a video which is preprocessed by ffmpeg. Briefly, I did the cropping and reencoding in ffmpeg with the following command :

  


  ffmpeg -i concat_output.avi -vf "crop=482:330:100:150" -c:v ffv1 test_crop.avi

  


  The output video was ok and can be normally playbacked in VLC player.

  


  But when I read the video in matlab, I found the frame read is distorted (see below image).
enter image description here

  


  I spended several hours in searching the similar issues posted online but found nothing. Can anyone give me some suggestions to get rid of this issue ? Thank you !

  


  The weirdest things :

  


  


  1. I did not find this problem in my uncropped raw video (concact_output.avi). This raw video is also encoded in ffv1.

     


  


  2. I did not find this problem if I did cropping but without reencoding with the following command :
ffmpeg -i concat_output.avi -vf "crop=482:330:100:150" test_crop2.avi

     


  


  


  In both of above cases I can have the normal image readout in matlab as shown below :

  


  enter image description here

  


• Is there an efficient way to use ffmpeg to perform a large quantity of cuts from a single file ?

  16 mars 2024, par Giuliano Oliveri

  I'm trying to cut video files into smaller chunks. (each one being one word said in the video, so they're not all of equal size)

  


  I've tried a lot of different approaches to try to be as efficient as possible, but I can't get the runtime to be under 2/3rd of the original video length. That's an issue because I'm trying to process 400+ hours of video.

  


  Is there a more efficient way to do this ? Or am I doomed to run this for weeks ?

  


  Here is the command for my best attempt so far

  


  ffmpeg -hwaccel cuda -hwaccel_output_format cuda -ss start_timestamp -t to_timestamp -i file_name -vf "fps=30,scale_cuda=1280:720" -c:v h264_nvenc -y output_file


  


  Note that the machine running the code has a 4090
This command is then executed via python, which gives it the right timestamps and file paths for each smaller clip in a for loop

  


  I think it's wasting a lot of time calling a new process each time, however I haven't been able to get better results with a split filter ; but here's the ffmpeg-python code for that attempt :

  


  Creation of the stream :

  


  inp = (
    ffmpeg
    .input(file_name, hwaccel="cuda", hwaccel_output_format="cuda")
    .filter("fps",fps=30)
    .filter('scale_cuda', '1280','720')
    .filter_multi_output('split')
)


  


  Which then gets called in a for loop

  


  (
    ffmpeg
    .filter(inp, 'trim', start=row[1]['start'], end=row[1]['end'])
    .filter('setpts', 'PTS-STARTPTS')
    .output(output_file,vcodec='h264_nvenc')
    .run()
)


  


• avfilter/drawtext : present 'hms' formatted 'pts' in 24h format

  7 mai 2018, par Vishwanath Dixit

  avfilter/drawtext : present 'hms' formatted 'pts' in 24h format
  HMS is formatted as HH:MM:SS.mmm, but, HH part is not limited to
  
  24 hours. For example, the the drawn text may look like this :
  
  243029:20:30.342. To present the timestamp in more readable and
  
  user friendly format, this patch provides an additional option
  
  to limit the hour part in the range 0-23.
  Note : Actually the above required format can be obtained with
  
  format options 'localtime' and 'gmtime', but,  milliseconds part
  
  is not supported in those formats.
  

  • [DH] doc/filters.texi
  • [DH] libavfilter/vf_drawtext.c