youtubePlaybackRate.js

/*
Youtube playback rate hotkeys:
Ctrl + UP
Ctrl + DONW
*/

function createPlaybackRateDisplay() {
    var elem = document.createElement('span');
    elem.style = 'position: fixed; left: 0; top: 0; z-index: 10000; background: #000; color: #fff; font-size: 32px;'
    elem.setAttribute('id', 'paylbackRateDisplay')
    elem.innerText = '';
    document.querySelector('body').appendChild(elem);
}

function destroyPlaybackRateDisplay() {
    try  {
        document.querySelector('#paylbackRateDisplay').remove();
    } catch (err) {
        
    }
}

function displayPlaybackRate() {
    var rate = document.getElementsByTagName("video")[0].playbackRate
    document.querySelector('#paylbackRateDisplay').innerText = Math.round(rate * 10)  / 10;
}

function playbackRateChange(e) {
    var video = document.getElementsByTagName("video")[0];
    var step = 0.2;

    if (e.ctrlKey && e.keyCode == 38) {
        video.playbackRate += step;
    }
    if (e.ctrlKey && e.keyCode == 40) {
        video.playbackRate -= step;
    }
    displayPlaybackRate();
}

destroyPlaybackRateDisplay();
createPlaybackRateDisplay();
displayPlaybackRate();
document.addEventListener('keyup', playbackRateChange, false);