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• I am trying to save frames from a webcam via Python and ffmpeg, but the video becomes way to fast

  10 mai 2022, par Matthias

  I get a stream of cv2 images from my webcam and want to save it to a video file. After playing a bit with cv2.VideoWriter() it turned out that using ffmpeg would provide more options and - apparently, following a few threads here on SO - lead to better results. So I gave the VidGear Python library a try, and it seems to work fine.

  


  There is one catch though : My webcam provides a variable framerate, most of the time between 10 and 30 FPS. When saving these frames the video file becomes way too fast, like watching in fast-forward. One real-time minute becomes only a few seconds in the video.

  


  I tried to play with various combinations of the ffmpeg's -framerate and/or -r parameters, but without luck. Here is the command I am using right now :

  


  ffmpeg -y -f rawvideo -vcodec rawvideo -s 1920x1080 -pix_fmt bgra -framerate 25.0 -i - -vcodec libx265 -crf 25 -r 25 -preset fast 


  


  For the records, I am creating the WriteGear class from the VidGear library like this :

  


  video_params = {
    "-vcodec": "libx265",
    "-crf": 25,
    "-input_framerate": 25,
    "-r": 25,
}
WriteGear(output_filename=video_file, logging=True, **video_params)


  


  Any ideas what I am doing wrong here and how I need to call ffmpeg ?

  


• Free music recognition API

  12 mars 2014, par AmirH

  I'm developing an application to recognize the music played by speakers. It records 32 seconds of the sound played and send a request via an API of music recognition. So far I used Echonest. But my api_key has been banned because of to many requests since I published my freeware, used by more than 200 users.

  So I looked for MusicBrainz but it needs the exact duration of the entire song to receive a acceptable response, duration that my application can't guess.

  So I'm looking for a free music recognition API so my freeware works. Do you know one ?

  Note : I used Echonest by :

  • capturing 32 seconds with ffmpeg

  • sending this command via cURL :

    curl -F "api_key=XXX" -F "filetype=mp3" -F "track=@sound.mp3" "http://developer.echonest.com/api/v4/track/upload" > info.txt

  I tried to use MusicBrainz by :

  • capturing 32 seconds with ffmpeg

  • generating the fingerprint using Chromaprint with this command :

    fpcalc sound.mp3 > fingerprint.txt

  • sending this command via cURL :

    curl -F "client=XXX" -F "meta=recordings" -F "duration=32" -F "fingerprint=ABC" "http://api.acoustid.org/v2/lookup" > info.txt

• ctrl+c doesn't wait for child process (background process) to finish with trap

  11 avril 2019, par phisch

  I have a script which registers a SIGINT trap and starts a ffmpeg background process that records part of the screen. The SIGINT trap sends a SIGINT signal to the background ffmpeg process to get it to gracefully stop and finish the recording.

  When this script is run in a terminal, and terminated from a separate terminal with kill -INT [SCRIPT_PID], the ffmpeg background process terminates gracefully and outputs confirmation in terminal 1.

  When the script is run in a terminal and stopped with ctrl+c the background process just dies instantly. (even if ctrl+c should just send a SIGINT signal)

  Why does ctrl+c behave differently than killing the script with kill -INT in this case ?
  How can i make sure the ffmpeg background process ends gracefully when ending the script with ctrl+c ?

  #!/bin/bash
  
  
  
  exit_script() {
  
      kill -INT $ffmpeg_pid
  
      wait $ffmpeg_pid
  
      printf "\n\nffmpeg should say 'exiting normally, received signal 2' before this message is printed!\n\n"
  
  }
  
  
  
  trap exit_script SIGINT 
  
  
  
  ffmpeg -f x11grab -s 500x500 -i :0.0+0,0 ~/video_`date +%s`.webm &
  
  ffmpeg_pid=$!
  
  
  
  wait

  edit : it seems like ffmpeg receives 2 int signals in the case of ctrl+c, but i don’t know why