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• lavfi : add a preinit callback to filters.

  31 juillet 2017, par Nicolas George

  lavfi : add a preinit callback to filters.
  It is necessary for filters with child objects, to set the class
  
  and default options values.
  

  • [DH] libavfilter/avfilter.c
  • [DH] libavfilter/avfilter.h

• NodeJS spawn ffmpeg thumb %t in filename

  7 septembre 2017, par asafg

  I’m creating screenshots at 15 fps with this NodeJS code :

  var spawn   = require('child_process').spawn;
  
  var args    = ['-ss', '00:00:07.86', '-i', 'filename.mp4', '-vf', 'fps=15', '/out%d.png'];
  
  var ffmpeg  = spawn('ffmpeg', args);

  This works fine, but I want the time stamp of each screenshot in the filename.

  from FFMPEG docs :

  %t is expanded to a timestamp

  But putting ... ,'/out%t.png'] fails and prints :

  grep stderr: [image2 @ 0x7f828c802c00] Could not get frame filename 
  
  number 2 from pattern '/Users/***/projects/out%t.png' (either set updatefirst or use a pattern like %03d within the filename pattern)
  
  av_interleaved_write_frame(): Invalid argument
  
  ...
  
  grep stderr: Conversion failed!
  
  
  
  child process exited with code 1

  So that doesn’t look like the way to go.

  How do i get the timestamp for each screenshot ?

  Thanks

• Kill an unresolved promise (or ignore and move on)

  17 septembre 2017, par Trees4theForest

  Using node child process exec, I’m calling a ffmpeg conversion via a promise that takes a bit of time. Each time the use clicks "next" it starts the FFMpeg command on a new file :

  function doFFMpeg(path){
  
    return new Promise((resolve, reject) => {
  
      exec('ffmpeg (long running command)', (error, stdout, stderr) => {
  
        if (error) {
  
          reject();
  
        }
  
      }).on('exit', (code) => { // Exit returns code 0 for good 1 bad
  
        if (code) {
  
          reject();
  
        } else {
  
          resolve();
  
        }
  
      });
  
    });
  
  }

  The problem is, if the user moves on to the next video before the promise is returned, I need to scrap the process and move on to converting the next video.

  How do I either :

  A) (Ideally) Cancel the current promised exec process*
  B) Let the current promised exec process complete, but just ignore that promise while I start a new one.

  *I realize that promise.cancel is not yet in ECMA, but I’d like to know of a workaround — preferably without using a 3rd party module / library.

  Attempt :

  let myChildProcess;
  
  
  
  function doFFMpeg(path){
  
  
  
    myChildProcess.kill();
  
  
  
    return new Promise((resolve, reject) => {
  
      myChildProcess = exec('ffmpeg (long running command)', (error, stdout, stderr) => {
  
        if (error) {
  
          reject();
  
        }
  
      }).on('exit', (code) => { // Exit returns code 0 for good 1 bad
  
        if (code) {
  
          reject();
  
        } else {
  
          resolve();
  
        }
  
      });
  
    });
  
  }