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• What should be the timing to capture screenshots as images and then convert the images to video file using ffmpeg ?

  22 juillet 2016, par TheLost Lostit

  I have a timer tick event where i take screenshots every 10ms

          int count = 0;
  
          private void timer1_Tick(object sender, EventArgs e)
  
          {
  
              Bitmap bmp = new Bitmap(sc.CaptureScreen());
  
              bmp.Save(@"D:\SavedScreenshots\screenshot" + count + ".bmp", System.Drawing.Imaging.ImageFormat.Bmp);
  
              bmp.Dispose();
  
              count ++;
  
          }

  Then i i’m using ffmpeg command line in command prompt window to create a video file from all the images :

  ffmpeg -framerate 2 -i screenshot%d.bmp -c:v libx264 -r 30  -pix_fmt yuv420p out.mp4

  Every bitmap file on hard disk it’s size is 7.91 MB
  The details : 1920x 1080 and Bit depth 32

  The problem is when making the ffmpeg command line with -framerate 2 then when i play the video file in windows media player it’s very very slow.
  When i saet the framerate to 10 then it’s too fast.
  When i set the framerate to 4 i’m getting error in yellow say too large.

  But maybe the problem is that i’m taking a screenshot every 10ms ? Maybe i should take a screenshot every 1000ms ? And then what should i change in the ffmpeg command line ?

  I want it to be like a regular video file speed. Not too fast and not too slow.
  What i’m capturing in the screenshot is my desktop screen and later i want to upload and show it to some support help in a forum.

• Can you think of a reason why windows might not enable audio if noone is logged in ?

  3 juillet 2017, par Caius Jard

  I’m having a bizarre problem with some virtual servers created to record podcasts. They run on amazon AWS as windows server 2012 instances and a small c# app tells FFMPEG to do the heavy lifting of capturing from the virtual screen and reading from the virtual sound card (Virtual Audio Cable : https://en.wikipedia.org/wiki/Virtual_Audio_Cable) via DirectShow filters

  The problem I have is if I leave the machine to do its stuff unattended, the recordings are sometimes silent. If I log in via VNC and watch it doing its stuff the audio is recorded just fine. All other aspects of the test op are the same, and the virtual machine is shut down between successive recordings so each one should theoretically be a clean slate. The app runs under a logged in session (hence the use of VNC rather than RDP)

  I’m now wondering if there is some optimisation of the windows sound engine whereby it doesn’t bother playing audio if it thinks noone is listening. The confusing thing to me is that not every virtual machine suffers these problems ; some of them record fine (and they’re all created from the same seed virtual hard disk image) in unattended mode

  I’m asking this question with the aim of getting together a list of things I can check/look into/debug.. I don’t have much knowledge of how MME/DirectSound/WASAPI work internally...

• FFMPEG command works in shell ! but not in my node.js

  29 juillet 2021, par Kuno Kim

  When my ffmpeg command is built by my node.js application it does not run.

  



  error

  



  Unrecognized option 'ss 3.2 -t 1.9 -i videoplayback.mp4 -vf  fps=15,scale=240:-1:flags=lanczos,palettegen palette.png'.


  



  command

  



  ffmpeg -ss 3.2 -t 1.9 -i videoplayback.mp4 -vf \ fps=15,scale=240:-1:flags=lanczos,palettegen palette.png


  



  this is my code

  



  var child_process = require('child_process')

function recordVideo() {

var spawn = child_process.spawn;

var args = [
    '-y', 
    '-ss', '3.2',
    '-t', '1.9', 
    '-i', '../getback/bin/videos/videoplayback.mp4', 
    '-vf', ' \\ ', 
    'fps=', '15', 
    'scale=', '320:-1', 
    'flags=','lanczos,palettegen palette.png', 
];



var ffmpeg = spawn('ffmpeg', args);

ffmpeg.stdout.on('data', function (data) {
    console.log(data);
});

ffmpeg.stderr.on('data', function (data) {
    console.log('grep stderr: ' + data);
});

ffmpeg.on('close', (code) => {
    console.log('child process exited with code ' + code);
}); 
};
recordVideo();


  



  what is this error ?
I think.. 'fps=', '15', In the following code 
 '=' options a problem.

  



  I am still learning English.
I'm sorry if it was hard to understand.