Wordpressのプラグインで、動画倍速ってないんですね。
これを元に開発しようかな。

動画（音声）を倍速にする機能（ボタンクリック）

index.html

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <title>Page Title</title>
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <script src="main.js"></script>
</head>
<body>
    <output id="res">
        <video src='/Users/matsumurashun/Downloads/pu-tyan.mp4' width='500' height='300' controls loop></video>
        <form>
            <input type="button" value="1倍速">
            <input type="button" value="2倍速">
            <input type="button" value="3倍速">
        </form>
    </output>    
</body>
</html>

main.js

window.onload = () => {
    const btn = document.getElementsByTagName("input");
    const video = document.getElementsByTagName("video")[0];

    btn[0].addEventListener('click', () => {
        video.playbackRate = 1.0;
        video.defaultPlaybackRate = 1.0;
    }, false);

    btn[1].addEventListener('click', () => {
        video.playbackRate = 2.0;
        video.defaultPlaybackRate = 2.0;
    }, false);

    btn[2].addEventListener('click', () => {
        video.playbackRate = 3.0;
        video.defaultPlaybackRate = 3.0;
    }, false);
}

動画（音声）を倍速にする機能（プルダウン選択）

index.html

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <title>Page Title</title>
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <script src="main.js"></script>
</head>
<body>
    <output id="res">
        <video src='/Users/matsumurashun/Downloads/pu-tyan.mp4' width='500' height='300' controls loop></video>
        <form>
            <select>
                <option value="1">1倍速</option>
                <option value="2">2倍速</option>
                <option value="3">3倍速</option>
            </select>
        </form>
    </output>    
</body>
</html>

main.js

window.onload = () => {
    const selector = document.getElementsByTagName("select")[0];
    selector.addEventListener('change', (it) => {
        video.playbackRate = setRate(it.target.value);
    });
    const setRate = (val) => {
        return Number(val);
    }
}

playbackRate:再生速度の倍率
Number:Numberオブジェクトで、引数に入れれば文字列を数値に変換してくれる