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• Issue with MJPEG stream playback speed when encoding with FFmpeg

  6 janvier, par Arciiix

  I'm working with a MJPEG stream source

  


  Stream #0:0: Video: mjpeg (Baseline), yuvj420p(pc, bt470bg/unknown/unknown), 1280x720 [SAR 1:1 DAR 16:9], 25 tbr, 25 tbn

  


  I want to capture this stream and save it to an MP4 file using FFmpeg, but I am running into a weird issue.

  


  The only way it works fine is when I just copy the stream without reencoding and using wallclock as timestamps (cmd 1) :

  


  ffmpeg -use_wallclock_as_timestamps 1 -i "http://IP/video/1280x720" -c:v copy output_good.mp4


  


  However, when I try encoding the stream with libx264, the playback speed of the resulting video becomes slower than 100%, causing the video to gradually fall out of sync with real-time. This happens even when I use any encoding, also when I explicitly set the frame rate or vsync. For example, these commands fail :

  


  

  • CMD 2 : ffmpeg -i "http://IP/video/1280x720" -c:v libx264 -r 30 -preset fast output_bad1.mp4

  


  • CMD 3 : ffmpeg -use_wallclock_as_timestamps 1 -i "http://IP/video/1280x720" -c:v libx264 output.mp4

  


  


  https://www.youtube.com/watch?v=PF0fuCu7Xao

  


  As you can see in the comparison of the resulting videos, the playback gradually slows down with CMD 2 and CMD 3, while it's alright with CMD 1.

  


  What I've noticed is that on the FFmpeg stdout, when using encoding, the speed= and FPS= go up and up, e.g. to 31 FPS even though my source is technically at 25 FPS.

  


  What I've tried :

  


  

  • different encoding codecs (e.g. libvpx)

  


  • -re

  


  • preset ultrafast on encoding

  


  • vsync (fps_mode), both ctr and vfr

  


  • fps=30 filter

  


  


  Has anyone encountered a similar issue or know how to force FFmpeg to preserve the correct playback speed while encoding or enforcing a frame rate ? Thanks !

  


• Change audio speed using ffmpeg node js

  26 juillet 2022, par Getwrong

  how do i change the speed of the song output using this function :

  



  function addAudio()
{
      console.log("adding audio...");

      ffmpeg()
      .videoCodec('libx264')
      .format('mp4')
      .outputFormat('mp4')
      .input(song)
      .input(video)
      .output(output1)
      .on('end', () => {                    
          resolve(output1);
      }).on('error', (_err) => {
          reject(_err);
      }).run();
}


  



  https://trac.ffmpeg.org/wiki/How%20to%20speed%20up%20/%20slow%20down%20a%20video

  



  this shows command line input but not sure how to use it in js function ?

  


• How to speed up the ffmpeg video compression in android ? [duplicate]

  27 février 2017, par Anantha Babu

  This question already has an answer here :

  • Fast Video Compression on Android
    
    2 answers
    

  I am using following command to compress video in android . But it takes more time. e.g for 1 min video it takes 50sec to compress.

  -y -i "+mInputPath+" -vf -s 640x480 -threads 5 -preset ultrafast -strict -2 "+mOutputPath.getAbsolutePath();

  Does anyone know how to increase speed ?