UserScript for controlling playback speed in Jellyfin

jellyfin.js

// ==UserScript==
// @name        Speed control - localhost:8096
// @namespace   Violentmonkey Scripts
// @include     http://localhost:8096/*
// @grant       none
// @version     1.0
// @author      -
// @description 1/30/2020, 12:16:50 AM
// ==/UserScript==

if(document.querySelector("body").innerText.indexOf("Value cannot be null") !== -1)
  location.href = "http://localhost:8096/";

let elem = document.createElement("input");
elem.type="range";
elem.value = 50;
elem.id="speedControl"
elem.addEventListener("change", e => {
  document.querySelector("video").playbackRate = e.target.value / 50;
});

const addRange = () => {
  const buttons = document.querySelector(".buttons");
  if (buttons && !document.querySelector("#speedControl")) {
    buttons.appendChild(elem);
  }
}

setInterval(addRange, 5000);