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• lavu/pixdesc : handle xv30be in av_[read|write]_image_line

  4 décembre 2022, par Philip Langdale

  lavu/pixdesc : handle xv30be in av_read_image_line
  xv30be is an obnoxious format that I shouldn't have included in the
  
  first place. xv30 packs 3 10bit channels into 32bits and while our
  
  byte-oriented logic can handle Little Endian correctly, it cannot
  
  handle Big Endian. To avoid that, I marked xv30be as a bitstream
  
  format, but while that didn't produce FATE errors, it turns out that
  
  the existing read/write code silently produces incorrect results, which
  
  can be revealed via ubsan.
  In all likelyhood, the correct fix here is to remove the format. As
  
  this format is only used by Intel vaapi, it's only going to show up
  
  in LE form, so we could just drop the BE version. But I don't want to
  
  deal with creating a hole in the pixfmt list and all the weirdness that
  
  comes from that. Instead, I decided to write the correct read/write
  
  code for it.
  And that code isn't too bad, as long as it's specialised for this
  
  format, as the channels are all bit-aligned inside a 32bit word.
  

  • [DH] libavutil/pixdesc.c

• swresample/resample : do not increase phase_count on exact_rational

  17 juin 2016, par Muhammad Faiz

  swresample/resample : do not increase phase_count on exact_rational
  high phase_count is only useful when dst_incr_mod is non zero
  
  in other word, it is only useful on soft compensation
  on init, it will build filter with low phase_count
  
  but when soft compensation is enabled, rebuild filter
  
  with high phase_count
  this approach saves lots of memory
  Reviewed-by : Michael Niedermayer <michael@niedermayer.cc>
  
  Signed-off-by : Muhammad Faiz <mfcc64@gmail.com>
  

  • [DH] libswresample/resample.c
  • [DH] libswresample/resample.h

• Is there an efficient way to use ffmpeg to create a huge quantity of small video file, cut from a larger one ?

  9 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()
)