Helios Player API

The <helios-player> Web Component allows you to embed and control Helios compositions in any web application. It handles loading the composition in an iframe and establishing a bridge for control and state management.

Quick Start

<script type="module" src="path/to/@helios-project/player/dist/index.js"></script>

<helios-player
  src="composition.html"
  width="1280"
  height="720"
  controls
  autoplay
  input-props='{"title": "My Video"}'
></helios-player>

API Reference

HTML Attributes

Attribute	Type	Description
src	string	URL of the composition (must contain Helios logic)
width	number	Display width (maintains aspect ratio if height also set)
height	number	Display height
controls	boolean	Show built-in playback controls (Play, Volume, Captions, Export)
controlslist	string	Space-separated list of features to hide: nodownload, nofullscreen
autoplay	boolean	Start playing immediately when ready
loop	boolean	Loop playback when finished
muted	boolean	Mute audio initially
poster	string	URL of an image to show before playback
preload	'auto' | 'none'	Preload behavior (default: 'auto')
interactive	boolean	Allow direct interaction with the iframe content (disables overlay)
input-props	JSON string	Pass initial properties to the composition
export-mode	'auto' | 'canvas' | 'dom'	Strategy for client-side export (default: 'auto')
export-format	'mp4' | 'webm'	Output format for client-side export (default: 'mp4')
export-caption-mode	'burn-in' | 'file'	How to handle captions during export (default: 'burn-in')
export-width	number	Width of the exported video (independent of display width)
export-height	number	Height of the exported video
export-bitrate	number	Target bitrate for export (bits/s)
export-filename	string	Filename for export (default: 'video')
disablepictureinpicture	boolean	Disable the Picture-in-Picture button
canvas-selector	string	CSS selector for the canvas element (default: 'canvas')
sandbox	string	Iframe sandbox flags (default: 'allow-scripts allow-same-origin')

CSS Variables (Theming)

You can customize the player's appearance using CSS variables:

helios-player {
  --helios-controls-bg: rgba(0, 0, 0, 0.8);
  --helios-text-color: #ffffff;
  --helios-accent-color: #ff0000;
  --helios-range-track-color: #555555;
  --helios-range-selected-color: rgba(255, 255, 255, 0.5);
  --helios-font-family: 'Helvetica', sans-serif;
}

JavaScript API

The element implements a Standard Media API-like interface for easy integration with video wrappers.

const player = document.querySelector('helios-player');

// Playback Control
player.play();
player.pause();
player.load();
player.requestPictureInPicture(); // Enter PiP mode
player.currentTime = 5.0; // Seek to 5 seconds
player.currentFrame = 150; // Seek to frame 150

// Audio Control
player.volume = 0.5; // 0.0 to 1.0
player.muted = true;

// Writable Properties
console.log(player.duration);     // Total duration in seconds
console.log(player.paused);       // Boolean
console.log(player.playbackRate); // Speed multiplier
console.log(player.fps);          // Composition FPS
console.log(player.loop);         // Loop state
console.log(player.autoplay);     // Autoplay state

// Read-Only Properties
console.log(player.videoWidth);   // Intrinsic width
console.log(player.videoHeight);  // Intrinsic height
console.log(player.readyState);   // 0-4 (HAVE_NOTHING to HAVE_ENOUGH_DATA)
console.log(player.networkState); // 0-3 (EMPTY, IDLE, LOADING, NO_SOURCE)
console.log(player.seeking);      // Boolean (true while scrubbing)
console.log(player.played);       // TimeRanges object of played segments
console.log(player.buffered);     // TimeRanges object of buffered segments
console.log(player.seekable);     // TimeRanges object of seekable segments
console.log(player.error);        // MediaError object if failed

// Input Props
player.inputProps = { title: "Updated Title" };

// Text Tracks
console.log(player.textTracks);
const track = player.addTextTrack("captions", "English", "en");

// Access active cues
track.addEventListener("cuechange", () => {
  console.log("Active Cues:", track.activeCues);
});

Events

The player dispatches standard media events:

• loadstart, loadedmetadata, loadeddata, canplay, canplaythrough
• play, pause, ended, playing
• timeupdate, seeking, seeked
• volumechange
• durationchange, ratechange
• error

Advanced Control

For low-level access to the Helios state, use getController().

const controller = player.getController();

if (controller) {
  const state = controller.getState();

  // Dynamic Updates
  controller.setDuration(30);       // Update duration to 30s
  controller.setFps(60);            // Update FPS to 60
  controller.setSize(1080, 1080);   // Update resolution
  controller.setMarkers([{ id: "m1", time: 5, label: "Intro" }]);
}

Diagnostics

View environment capabilities (WebCodecs, WebGL) by pressing Shift+D to toggle the overlay, or calling diagnose() programmatically.

const report = await player.diagnose();
console.log("WebCodecs support:", report.webCodecs);

Captions

You can provide captions by adding a <track> element as a child.

<helios-player src="...">
  <track kind="captions" src="captions.srt" default>
</helios-player>

The player will fetch the SRT file and pass it to the Helios controller.

Client-Side Export

The player supports exporting videos directly in the browser (using VideoEncoder).

1. Formats: Supports mp4 (H.264/AAC) and webm (VP9/Opus).
2. Audio: Captures audio from <audio> elements (must be CORS-enabled).
3. Captions: Supports "burning in" captions (export-caption-mode="burn-in") or saving as sidecar file (export-caption-mode="file").
4. Resolution: Configure export resolution independently of player size using export-width and export-height.
5. Usage: User clicks "Export" in controls, or call clientSideExporter manually (internal API).

UI Features

• Captions: Toggle "CC" button to overlay active captions.
• Volume: Slider and Mute toggle.
• Speed: Selector for playback rate (0.25x - 2x).
• Fullscreen: Toggle fullscreen mode.
• Scrubber: Visual playback range indication.
• Responsive: Controls adapt to small widths (compact/tiny modes).

Common Issues

• Cross-Origin (CORS): The player uses an iframe. If the src is on a different origin, ensure CORS headers are set.
• Audio Export: Audio elements must serve data with Access-Control-Allow-Origin to be captured by the exporter.

Source Files

• Component: packages/player/src/index.ts
• Exporter: packages/player/src/features/exporter.ts