node-fluent-ffmpeg - Execute Custom FFMPEG arguments hack

fluent-ffmpeg-custom-args.js

/*
  As at the time of writing this Fluent ffmpeg-API for node.js has not been updated 
  for years and still does not support custom FFMPEG attributes, the only solutions
  are either forking it or resorting to hacks like this one...

  Please use it only when fluent does not support more complex arguments 
  (like generating multi-rendition HLS with all playlists in a single command)
  
  NOTE: this does not support 'progress' event, but you can do it easily by
  parsing 'stderr' event with extractProgress method from fluent-ffmpeg/lib/options.js
*/

const fluent = require('fluent-ffmpeg');

const executeFfmpeg = args => {
    let command = fluent().output(' '); // pass "Invalid output" validation
    command._outputs[0].isFile = false; // disable adding "-y" argument
    command._outputs[0].target = ""; // bypass "Unable to find a suitable output format for ' '"
    command._global.get = () => { // append custom arguments
        if(typeof args === "string") {
            return args.split(' ').filter(c => c !== "" && c !== "\\\n")
        } else return args;
    };
    return command;
};

executeFfmpeg('-f lavfi -i testsrc=size=1920x1080:rate=30 -y -t 60 ./test.mp4')
    .on('start', commandLine => console.log('start', commandLine))
    .on('codecData', codecData => console.log('codecData', codecData))
    .on('error', error => console.log('error', error))
    .on('stderr', stderr => console.log('stderr', stderr))
    .run();