discord.js/src/client/voice/pcm/FfmpegConverterEngine.js

const ConverterEngine = require('./ConverterEngine');
const ChildProcess = require('child_process');

function chooseCommand() {
  for (const cmd of ['ffmpeg', 'avconv', './ffmpeg', './avconv']) {
    if (!ChildProcess.spawnSync(cmd, ['-h']).error) {
      return cmd;
    }
  }
}

class FfmpegConverterEngine extends ConverterEngine {
  constructor(player) {
    super(player);
    this.command = chooseCommand();
  }

  createConvertStream() {
    super.createConvertStream();
    const encoder = ChildProcess.spawn(this.command, [
      '-analyzeduration', '0',
      '-loglevel', '0',
      '-i', '-',
      '-f', 's16le',
      '-ar', '48000',
      '-ss', '0',
      'pipe:1',
    ], { stdio: ['pipe', 'pipe', 'ignore'] });
    encoder.on('error', console.log);
    encoder.stdin.on('error', console.log);
    encoder.stdin.on('error', console.log);
    return encoder;
  }
}

module.exports = FfmpegConverterEngine;