Etro Overview

In Etro, the movie is a context for adding and rendering content. It holds a list of layers and effects. A layer is a piece of video and/or audio content with a list of effects.


To create a movie that will render to the outputCanvas:

var movie = new etro.Movie({ canvas: outputCanvas })

The movie can then be played or recorded. Playing renders the movie to the canvas and audio context, and it can be interrupted with pause. Recording renders the movie and saves the result to a video blob.
// or
movie.record({ frameRate: 30 }).then(blob => /*do something with `blob`*/)

See the Movie documentation.


Layers are pieces of content for the movie, such as video and audio clips and titles:

// The base visual layer renders a solid rectangle filling its bounds
var layer1 = new etro.layer.Visual({ startTime: 0, duration: 3 })
// The video layer extends the visual layer and renders an html video element
var layer2 = new etro.layer.Video({ startTime: 3, source: htmlVideoEl })
movie.layers.push(layer1, layer2)  // the same as calling movie.addLayer

There are a number of built-in layers, but you can also subclass any of them and create your own.


Effects alter a layer or movie's output. Currently, only visual effects are supported. Audio can be manipulated using the web audio API (see Audio). Etro offers a set of built-in effects that can be used like this:

var effect = new etro.effect.Contrast(2.0)

You can also create your own visual effects by subclassing a base effect class. If you want to make a hardware-acclerated effect that uses GLSL, subclass etro.effect.Shader. If you want to make any other type of visual effect, subclass etro.effect.Base directly.

Example of a custom effect:

class MyEffect extends etro.effect.Base {
    constructor(width, height) {
        this.width = width
        this.height = height
     * @param {(etro.Movie|etro.layer.Visual)} target
    apply(target) {
        target.vctx.fillStyle = 'red'
        target.vctx.fillRect(0, 0, this.width, this.height)

layer.addEffect(new MyEffect(100, 100))