script.js

var video = document.getElementById("rick")
var startTime = 1570815649091

video.addEventListener('loadedmetadata', function() {
  video.play()

  jumpToLocation()

  video.addEventListener('play', function() {
    console.log("Playing.")

    window.setTimeout(sync, 2000)
  })
})

function jumpToLocation() {
  var difference = Date.now() - startTime
  var currentTime = (difference / 1000) % video.duration

  video.currentTime = currentTime
}

function restorePlaybackRate() {
  console.log("Restoring normal speed and waiting 10 seconds.")

  video.playbackRate = 1.0

  window.setTimeout(sync, 10000)
}

function sync() {
  console.log("Syncing.")

  var difference = Date.now() - startTime
  var currentTime = (difference / 1000) % video.duration

  console.log("Video should be " + currentTime)
  console.log("Video is " + video.currentTime)

  var offset = currentTime - video.currentTime

  console.log("Offset is " + offset)


  if (offset > 1) {
    console.log("Offset too big. Jumping.")

    jumpToLocation()

    window.setTimeout(sync, 2000)
  }
  else if (offset > 0.1) {
    console.log("Speeding up a lot.")

    video.playbackRate = 1.1

    var delay = Math.round(offset * 10 * 1000)

    console.log("Waiting " + (delay / 1000))

    window.setTimeout(restorePlaybackRate, delay)
  }
  else if (offset < -0.1) {
    console.log("Slowing down a lot.")

    video.playbackRate = 0.9

    var delay = Math.round(offset * -10 * 1000)

    console.log("Waiting " + (delay / 1000))

    window.setTimeout(restorePlaybackRate, delay)
  }
  else if (offset > 0.01) {
    console.log("Speeding up a little bit.")

    video.playbackRate = 1.01

    var delay = Math.round(offset * 100 * 1000)

    console.log("Waiting " + (delay / 1000))

    window.setTimeout(restorePlaybackRate, delay)
  }
  else if (offset < -0.01) {
    console.log("Slowing down a little bit.")

    video.playbackRate = 0.99

    var delay = Math.round(offset * -100 * 1000)

    console.log("Waiting " + (delay / 1000))

    window.setTimeout(restorePlaybackRate, delay)
  }
  else {
    console.log("Timing good. Waiting 10 seconds.")

    window.setTimeout(sync, 10000)
  }
}