fluent-ffmpeg get codec data without specifying output

Question

I am using fluent-ffmpeg node module for getting codec data from a file. It works if I give an output but I was wondering if there is any option to run fluent-ffmpeg without giving to it an output. This is what I am doing:

readStream.end(new Buffer(file.buffer));
var process = new ffmpeg(readStream);

process.on('start', function() {
  console.log('Spawned ffmpeg');
}).on('codecData', function(data) {
  //get recording duration
  const duration = data.duration;
  console.log(duration)
}).save('temp.flac');

As you can see I am saving the file to temp.flac so I can get the seconds duration of that file.

Answer 1

If you don't want to save the ffmpeg process result to a file, one thing that comes to mind is to redirect the command output to /dev/null.

In fact, as the owner of the fluent-ffmpeg repository said in one comment, there is no need to specify a real file name for the destination when using null format.

So, for example, something like that will work:

let process = new ffmpeg(readStream);

process
  .addOption('-f', 'null')  // set format to null 
  .on('start', function() {
    console.log('Spawned ffmpeg');
  })
  .on('codecData', function(data) {
    //get recording duration
    let duration = data.duration;
    console.log(duration)
  })
  .output('nowhere')  // or '/dev/null' or something else
  .run()

It remains a bit hacky, but we must set an output to avoid the "No output specified" error.