HTML/JavaScript で Web ページを開いている間スリープを防止する方法 [PC/iOS/Android対応]

Web を開いている間、スリープを防止する方法です。デスクトップ、モバイルともに対応しているはずです。
ユーザーが何かをクリックした後有効になるので、適当なボタンでも設置してクリックさせてください。

Chrome 73.0.3683.86、macOS 10.14.3 Safari 12.0.3、iOS 12.2 Safari & Chrome、Android Chrome で動作確認済み。
他の環境で動いた / 動かないなどあればコメントで教えてください。

HTML

<video style="display: none;" muted autoplay id="sleep-prevent-video-ios" playsinline>
  <!-- For iOS -->
  <source src="data:video/mp4;base64,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</video>
<video style="display: none;" muted autoplay id="sleep-prevent-video-android" playsinline>
  <!-- For Android -->
  <source src="data:video/mp4;base64,AAAAIGZ0eXBpc29tAAACAGlzb21pc28yYXZjMW1wNDEAAAAIZnJlZQAAAzttZGF0AAAC8AYF///s3EXpvebZSLeWLNgg2SPu73gyNjQgLSBjb3JlIDE0OCByMjcyMSAtIEguMjY0L01QRUctNCBBVkMgY29kZWMgLSBDb3B5bGVmdCAyMDAzLTIwMTYgLSBodHRwOi8vd3d3LnZpZGVvbGFuLm9yZy94MjY0Lmh0bWwgLSBvcHRpb25zOiBjYWJhYz0xIHJlZj0yIGRlYmxvY2s9MTowOjAgYW5hbHlzZT0weDE6MHgxMzEgbWU9aGV4IHN1Ym1lPTcgcHN5PTEgcHN5X3JkPTEuMDA6MC4wMCBtaXhlZF9yZWY9MCBtZV9yYW5nZT0xNiBjaHJvbWFfbWU9MSB0cmVsbGlzPTEgOHg4ZGN0PTAgY3FtPTAgZGVhZHpvbmU9MjEsMTEgZmFzdF9wc2tpcD0xIGNocm9tYV9xcF9vZmZzZXQ9LTIgdGhyZWFkcz0yIGxvb2thaGVhZF90aHJlYWRzPTEgc2xpY2VkX3RocmVhZHM9MCBucj0wIGRlY2ltYXRlPTEgaW50ZXJsYWNlZD0wIGJsdXJheV9jb21wYXQ9MCBjb25zdHJhaW5lZF9pbnRyYT0wIGJmcmFtZXM9MyBiX3B5cmFtaWQ9MCBiX2FkYXB0PTEgYl9iaWFzPTAgZGlyZWN0PTAgd2VpZ2h0Yj0xIG9wZW5fZ29wPTAgd2VpZ2h0cD0yIGtleWludD0xMDAga2V5aW50X21pbj0xMCBzY2VuZWN1dD00MCBpbnRyYV9yZWZyZXNoPTAgcmNfbG9va2FoZWFkPTQwIHJjPWFiciBtYnRyZWU9MSBiaXRyYXRlPTE1MDAgcmF0ZXRvbD0xLjAgcWNvbXA9MC42MCBxcG1pbj0xMCBxcG1heD02OSBxcHN0ZXA9NCB2YnZfbWF4cmF0ZT0yNDAwIHZidl9idWZzaXplPTI0MDAwIG5hbF9ocmQ9bm9uZSBmaWxsZXI9MCBpcF9yYXRpbz0xLjQwIGFxPTM6MS4wMACAAAAAO2WIhAAh//7hA/gU2Rk+YwbX7z3hwlUdq5XF1uz05CyTBQQ1XutfXipNv8c0sLqenwjUUbwHF4deeqdxAAAC/G1vb3YAAABsbXZoZAAAAADVH5Y71R+WOwAAA+gAAABkAAEAAAEAAAAAAAAAAAAAAAABAAAAAAAAAAAAAAAAAAAAAQAAAAAAAAAAAAAAAAAAQAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAIAAAImdHJhawAAAFx0a2hkAAAAA9UfljvVH5Y7AAAAAQAAAAAAAABkAAAAAAAAAAAAAAAAAAAAAAABAAAAAAAAAAAAAAAAAAAAAQAAAAAAAAAAAAAAAAAAQAAAAAA+AAAAPgAAAAAAJGVkdHMAAAAcZWxzdAAAAAAAAAABAAAAZAAAAAAAAQAAAAABnm1kaWEAAAAgbWRoZAAAAADVH5Y71R+WOwAAKAAAAAQAVcQAAAAAAC1oZGxyAAAAAAAAAAB2aWRlAAAAAAAAAAAAAAAAVmlkZW9IYW5kbGVyAAAAAUltaW5mAAAAFHZtaGQAAAABAAAAAAAAAAAAAAAkZGluZgAAABxkcmVmAAAAAAAAAAEAAAAMdXJsIAAAAAEAAAEJc3RibAAAAKVzdHNkAAAAAAAAAAEAAACVYXZjMQAAAAAAAAABAAAAAAAAAAAAAAAAAAAAAAA+AD4ASAAAAEgAAAAAAAAAAQAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAABj//wAAAC9hdmNDAU1AKf/hABhnTUAp6YhPVYCIAAADAAgAAAMAoHjBicABAARo6uyyAAAAEHBhc3AAAAABAAAAAQAAABhzdHRzAAAAAAAAAAEAAAABAAAEAAAAABxzdHNjAAAAAAAAAAEAAAABAAAAAQAAAAEAAAAUc3RzegAAAAAAAAMzAAAAAQAAABRzdGNvAAAAAAAAAAEAAAAwAAAAYnVkdGEAAABabWV0YQAAAAAAAAAhaGRscgAAAAAAAAAAbWRpcmFwcGwAAAAAAAAAAAAAAAAtaWxzdAAAACWpdG9vAAAAHWRhdGEAAAABAAAAAExhdmY1Ny41Ny4xMDA=">
</video>

JavaScript

document.addEventListener('click', function() {
  document.getElementById('sleep-prevent-video-ios').play();
  document.getElementById('sleep-prevent-video-android').play();
});

setInterval(function(){
  document.getElementById('sleep-prevent-video-ios').play();
  document.getElementById('sleep-prevent-video-android').play();
}, 20000);  // 20秒ごと

playsinline とは？

モバイルで、動画がフルスクリーンで再生されるのを防ぎます。
https://webkit.org/blog/6784/new-video-policies-for-ios/

On iPhone, elements will now be allowed to play inline, and will not automatically enter fullscreen mode when playback begins.
elements without playsinline attributes will continue to require fullscreen mode for playback on iPhone.
When exiting fullscreen with a pinch gesture, elements without playsinline will continue to play inline.

playsinline が指定されていないとデフォルトではフルスクリーンで再生されます。

自動再生ポリシー

初回はユーザーからのアクションによって再生する必要があります。
2回目以降は JavaScript で可能です。
https://developers.google.com/web/updates/2017/09/autoplay-policy-changes

Chrome's autoplay policies are simple:
Muted autoplay is always allowed.
Autoplay with sound is allowed if:

• User has interacted with the domain (click, tap, etc.).
• On desktop, the user's Media Engagement Index threshold has been crossed, meaning the user has previously play video with sound.
• On mobile, the user has [added the site to their home screen].
  Top frames can delegate autoplay permission to their iframes to allow autoplay with sound.

Wake Lock API

Wake Lock API というのが最近出たようですがまだ実装しているブラウザは少ないようですね。
https://www.w3.org/TR/wake-lock/
https://www.chromestatus.com/feature/4636879949398016

参考

https://qiita.com/46neko/items/445b01bf563ebed0c16e
https://stackoverflow.com/questions/9709891/prevent-ios-mobile-safari-from-going-idle-auto-locking-sleeping
https://webkit.org/blog/6784/new-video-policies-for-ios/
https://qiita.com/uhyo/items/f72edd71e4601768ff25