Code for https://youtu.be/4doWq-uSa60. Since this is using pipe, use it like `node . > out.mp4`.

index.js

'use strict';

const { writeFileSync, unlinkSync } = require(`fs`);
const ffmpeg = require(`fluent-ffmpeg`);
const { stringify } = require(`subtitle`);
const syllable = require(`syllable`);

const words = `
_l1_Hi _l1_there!
My name is _l2_Ben
I am a computer science student at _l1_UPI
_w1_
I would like to have Developer Student Club on my campus
because I think Google brand would motivate people to join
and thus provoke an active community
_w1_
I believe a good community is a key for improvement
and developer club might be a nice way to do it
_w1_
I'm familiar with Google services JavaScript and web technology
I think that qualify me to be a lead for this club
_w1_
Well that's a bit about me
_l1_bye!
_l3_:)
`.split(/\s/).filter(x => !!x);

{
  let start = 800;
  const wait = 500;
  const mult = 50;
  let subs = [];
  for (let text of words) {
    let match = text.match(/_(\D+)(\d+)_(.*)/);
    let end = start + syllable(text) * 50 + 250;

    if (match) {
      switch(match[1]) {
        case `w`:
          start += Number(match[2]) * wait;
          continue;
          break;
        case `l`:
          text = match[3];
          end += Number(match[2]) * wait;
          break;
      }
    }

    subs.push({
      start,
      end,
      text,
    });
    start = end;
  }
  writeFileSync(`subtitle.srt`, stringify(subs));
}

ffmpeg(`audio.m4a`)
  .input(`color=c=EEDDDD:size=1280x500:d=36`)
  .inputFormat(`lavfi`)
  .videoFilter(`subtitles=subtitle.srt:force_style='FontSize=128,PrimaryColour=&H00111111,Alignment=10'`)
  .format(`nut`)
  .stream(process.stdout)

package.json

{
  "dependencies": {
    "fluent-ffmpeg": "^2.1.2",
    "subtitle": "^1.0.1",
    "syllable": "^3.0.0"
  },
  "license": "MIT",
  "author": "Ben N <bentinata@gmail.com>"
}