Jumpcutter, like carykh's.

jumpcutter.js

(function () {
  let a = new AudioContext
  let V = document.querySelector('video')
  let v = a.createMediaElementSource(V)
  let SP = a.createScriptProcessor(256, 1, 1)
  let counter = 0
  let scriptName = 'JUMPCUTTER'

  window[scriptName] = {
    threshold: 0.001,
    silentSpeed: 4,
    talkingSpeed: 1.5,
    silentDebounceLimit: 100,
    talkingDebounceLimit: 3,
    volumeGain: 1,
    delay: 0
  }

  let isTalking = true

  SP.onaudioprocess = evt => {
    const scriptInfo = window[scriptName]
    const threshold = scriptInfo.threshold
    const silentSpeed = scriptInfo.silentSpeed
    const talkingSpeed = scriptInfo.talkingSpeed
    const silentDebounceLimit = scriptInfo.silentDebounceLimit
    const talkingDebounceLimit = scriptInfo.talkingDebounceLimit

    if (V.paused) {
      counter = -100
      if (V.playbackRate !== talkingSpeed) {
        V.playbackRate = talkingSpeed
      }
      return
    }

    let data = evt.inputBuffer.getChannelData(0)
    let total = 0
    let len = data.length
    for (let i = 0; i < len; i++) total += Math.abs(data[i])
    total = total / len
    isTalking = total > threshold

    const speed = isTalking ? talkingSpeed : silentSpeed
    if (V.playbackRate !== speed) {
      counter++
    } else if (isTalking) {
      counter = 0
    }

    const debounceLimit = isTalking ? talkingDebounceLimit : silentDebounceLimit
    if (counter > debounceLimit){
      if (V.playbackRate !== speed) {
        console.log('New speed:', speed)
        V.playbackRate = speed
      }
      counter = 0
    }

    g.gain.value = scriptInfo.volumeGain
    d.delayTime.value = scriptInfo.delay
  }

  d = a.createDelay(30)
  v.connect(d)
  g = a.createGain()
  d.connect(g)
  g.connect(a.destination)

  v.connect(SP)
  SP.connect(a.destination)
}())