ass-html5

Display ASS/SSA subtitles on html5 videos

Table of Contents

• ass-html5
  • Table of Contents
  • Installation
  • Features
  • Usage
    • Options
    • Simple HTML
    • Svelte and Plry
    • videojs
• Credits

Installation

pnpm add ass-html5

Features

• Karaoke Support: Full support for \k, \kf, \ko, and \K tags.
• Vector Drawings: High-performance rendering of ASS vector paths (\p) using Path2D.
• Clipping: Support for rectangular and vector clipping/masking (\clip, \iclip).
• Advanced Transformations:
  • Rotation around all axes (\frz, \frx, \fry).
  • Scaling (\fscx, \fscy) and Shearing (\fax, \fay).
  • Custom rotation origin (\org).
• Smart Wrapping: Implementation of \q styles for optimal line breaking.
• Collision Handling: Automatic vertical shifting to prevent overlapping subtitles.
• Blur Effects: Edge blur (\be) and Gaussian blur (\blur) using Canvas filters.
• Performance Optimized: Built-in layer caching to minimize redundant redraws.

Usage

Options

option	description	required	type	default
assText	The ass text string	🚫	string	undefined
subUrl	URL to fetch the ASS content from	🚫	string	undefined
video	The video to display the subtile on. Can be either an HTMLVideoElement or string (html query selector )	✅	HTMLVideoElement / string	undefined
font_urls	Custom fonts url load	🚫	string[]	undefined
zIndex	zIndex of the rendering frame	🚫	number	Drawn after the video
onReady	A Callback that is invoked when the preprocess of the ass text by render is done	🚫	() => void	undefined
logging	Type of logging	🚫	LOGTYPE	LOGTYPE.DISABLE

One of assText or subUrl is required.

Simple HTML

Note

In fullscreen, the browser only shows the video element and its controls, so the subtitles move to the top layer with the Popover API. That needs Chrome 114+, Firefox 125+ or Safari 17+. On iPhone the video uses its own fullscreen player, so subtitles are not shown there.

Subtitles that reach the bottom of the frame are drawn over the native control bar. Players with their own controls, like video.js or plyr (example), keep the controls above the subtitles.

<script src="https://cdn.jsdelivr.net/npm/ass-html5@latest/dist/ass.min.js"></script>

<video src="/assets/video.mp4" id="video" controls></video>

<script>
  document.addEventListener('DOMContentLoaded', async () => {
    // Using subUrl to fetch subtitle automatically
    const ass = new ASS.default({
      subUrl: '/assets/video.ass',
      video: document.getElementById('video')
    });
    await ass.render();

    // You can switch subtitles dynamically:
    // await ass.setSubUrl('/assets/other.ass');
    // OR
    // await ass.setAssText('[Script Info]...');
  });
</script>

Svelte and Plry

<script lang="ts">
    import video from '$lib/assets/video.mp4'
    import cc from '$lib/assets/cc.ass?url'
    import ASS from 'ass-html5'
    import { onMount } from 'svelte';
    import Plyr from 'plyr'

    const ass = new ASS({
        subUrl: cc,
        video: "#video-test"
    })

    let vidElement: HTMLVideoElement
    let player: Plyr
    onMount(async () => {
        player = new Plyr(vidElement)
        await ass.render()
    })

</script>

<div class="video-container">
    <!-- svelte-ignore a11y-media-has-caption -->
    <video
        preload="metadata"
        src="{video}"
        id="video-test"
        controls
        autoplay
        class="vid"
        bind:this={vidElement}
    ></video>
</div>

videojs

In the head :

<script src="https://cdn.jsdelivr.net/npm/ass-html5@latest/dist/ass.min.js" defer></script>
<script src="https://vjs.zencdn.net/8.3.0/video.min.js" defer></script>
<link href="https://vjs.zencdn.net/8.3.0/video-js.css" rel="stylesheet" />

In the body :

<video
  id="my-video"
  class="video-js"
  controls
  preload="auto"
  width="1280"
  height="720"
  data-setup="{}"
>
  <source src="assets/video.mp4" type="video/mp4" />
</video>

In the script tag :

<script>
  document.addEventListener('DOMContentLoaded', async () => {
    let res = await fetch('/assets/video.ass');
    let assSubs = await res.text();

    var player = videojs('my-video');

    player.ready(async () => {
      // Get the video element from the player
      var videoElement = player.el().getElementsByTagName('video')[0];
      const ass = new ASS.default({
        assText: assSubs,
        video: videoElement
      });
      await ass.render();
    });
  });
</script>

---

Credits

Thanks to the ass-compiler by weizhenye.