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• matroskaenc : write correct Display{Width, Height} in stereo encoding

  22 octobre 2014, par Vittorio Giovara

  matroskaenc : write correct DisplayWidth, Height in stereo encoding
  should be the raw amount of pixels (for example 3840x1080 for full HD side by
  
  side) and the DisplayWidth/Height in pixels should be the amount of pixels for
  
  one plane (1920x1080 for that full HD stream)."
  So, move the aspect ratio check in the mkv_write_stereo_mode() function
  
  and always write the embl when stereo format and/or aspect ration is set.
  
  Also add a few comments to that function.
  CC : libav-stable@libav.org
  
  Found-by : Asan Usipov <asan.usipov@gmail.com>
  

  • [DH] libavformat/matroskaenc.c

• How much the duration of an mp3 file given by Ffprobe is precise ?

  24 septembre 2024, par Julien Larget-Piet

  I have an mp3 file at a sample rate value of 44100, let's name it a.mp3.

  


  So i get the duration of a.mp3 with the following ffprobe command :

  


  ffprobe -v error -show_entries format=duration -of default=noprint_wrappers=1:nokey=1 a.mp3

  


  I get 7.752 seconds.

  


  Because the sample rate is per second, in theory the total amount of samples should be,

  


  44100 * 7.752 = 341863.2

  


  Let's round it to 341863

  


  But using python library ffmpegio with the following code, i get a total amount of sample equal to 340560.

  


  with ffmpegio.open(file, 'ra', blocksize = 16, sample_fmt = 'dbl') as file_opened:

        for i, indata in enumerate(file_opened):

            do some stuff
    print(i * 16)


  


  So there is a non-negligible difference between 341863 and 340560.

  


  I think it comes from the duration value given by Ffmpeg.
What do you thin ?

  


  I search in ffmpegio documentation, but found nothing that trigered my attention :

  


  https://python-ffmpegio.github.io/python-ffmpegio/

  


  Thanks.

  


  Search for answers about the precision of the ffprobe command.

  


• get consistent 60fps while recording X screen with ffmpeg

  28 janvier 2021, par thelmuxkriovar

  I wrote the following script to record an X screen for a specified amount of time, to make sure that it's lossless I've separated it into two steps

  


  

  1. record for the specified amount in a codec that requires almost no compression (so there's no overhead that might cause frames to be dropped)

  


  2. re-encode the original video into HEVC to make the filesize significantly smaller

  


  


  ffmpeg -hwaccel cuda -hwaccel_output_format cuda -vsync 1 -f x11grab -probesize 128M -s 1920x1080 -r 60 -i :0.0 -qscale 0 -vcodec huffyuv -t 00:01:13 "$video.avi" # record the screen losslessly
ffmpeg -hwaccel cuvid -vsync 1 -i "$video.avi" -map 0:0 -c:v:0 hevc_nvenc -crf 23 -preset medium "$video-clean.mp4"


  


  This works just like I expect it to some of the time, but very often it drops a lot of frames (I've seen as many as 10000 frames dropped on occasion)

  


  The gpu is a 1080 TI that's being used just for rendering an X server with a chrome window and recording it, according to nvidia-smi the usage never goes to higher than 50% even in the most extreme cases.

  


  I don't know what else to try, I thought about using a ramdisk to write the file to as it might be an IO problem, but ffmpeg refuses to write to tmpfs (for some reason I can't explain)