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• Create VHS Hi-Fi type (20Hz-20kHz) WAV file, from a 48kHz source FFmpeg [closed]

  27 août 2023, par Taymur Roshan

  I've been experimenting with using FFmpeg to convert modern high-quality audio (44.1, 48 & 96kHz etc.)into analogue type audio which are the old fashions Hi-Fi sounds like the 20 kHz frequency sampling signals https://en.wikipedia.org/wiki/VHS#Hi-Fi_audio_system.

  


  But since I already figured out of how to simply convert high frequency (source 48kHz) to low frequently (output 20kHz) using the '-ar' filter :

  


  ffmpeg -i "source.webm" -c:a pcm_s16le -ar 20000 "output.wav"


  


  However what I would like to know is that how can I make a genuine "flat full-range frequency response" 20 Hz to 20 kHz ?

  


  That would mean first downmix to 20kHz and also remove the first 20Hz out of the audio.

  


• Fastest way to generate thumbnails with FFMPEG

  10 mai 2022, par Pit Digger

  FFMPEG takes 9 minutes for generating thumbnails every 15 seconds of a 3 hour long video. What is fastest way to do this ? I have tried following combinations but its taking same time.

  


  ffmpeg -ss 0.0 -t 10800 -i test.mp4 -an -vsync cfr -vf fps=1000/15000 -s 128x72 -f image2 -c:v png -compression_level 100 temp-%010d.png

ffmpeg -i test.mp4 -f image2 -bt 20M -vf fps=1/15 thumbs/tv%03d.png

ffmpeg -i inputvideo.mp4 -vf "select='not(mod(n,450))',setpts='N/(30*TB)'" -f image2 thumbnail%03d.jpg


  


  https://trac.ffmpeg.org/wiki/Create%20a%20thumbnail%20image%20every%20X%20seconds%20of%20the%20video

  


• shell_exec echo'ing too fast or too late

  15 septembre 2016, par root

  So I read throug this article : https://trac.ffmpeg.org/wiki/PHP
  and found this :

  <?php
  
  echo "Starting ffmpeg...\n\n";
  
  echo shell_exec("ffmpeg -i input.avi output.avi >/dev/null 2>/dev/null &");
  
  echo "Done.\n";

  the code works almost perfectly fine, but the only thing that bothers me is, that because the shell_exec is being executed in the background (so there is no loading sign on the tab the whole time) all the echo’s are being executed immediatly. This means, that the "Done" echo is being written before ffmpeg finished its task.

  But when I remove the ’&’ the site does also what it is intended to do but now it waits until the shell_exec is finished until it echo’s out the "Starting ffmpeg..."

  So I kinda have the problem of figuring out how to get to such an order :

  1) echo something
  2) execute commad and wait until its finished.
  3) echo again

  I am a total beginner to php but have experience in programming overall. Please have mercy.

  Thank you for your time !