canvas-record

Record a video in the browser or directly on the File System from a canvas (2D/WebGL/WebGPU) as MP4, WebM, MKV, GIF, PNG/JPG Sequence using WebCodecs and Wasm when available.

Installation

npm install canvas-record

Usage

import { Recorder, RecorderStatus, Encoders } from "canvas-record";
import createCanvasContext from "canvas-context";

// Setup
const pixelRatio = devicePixelRatio;
const width = 512;
const height = 512;
const { context, canvas } = createCanvasContext("2d", {
  width: width * pixelRatio,
  height: height * pixelRatio,
  contextAttributes: { willReadFrequently: true },
});
Object.assign(canvas.style, { width: `${width}px`, height: `${height}px` });

const mainElement = document.querySelector("main");
mainElement.appendChild(canvas);

// Animation
let canvasRecorder;

function render() {
  const width = canvas.width;
  const height = canvas.height;

  const t = canvasRecorder.frame / canvasRecorder.frameTotal || Number.EPSILON;

  context.clearRect(0, 0, width, height);
  context.fillStyle = "red";
  context.fillRect(0, 0, t * width, height);
}

const tick = async () => {
  render();

  if (canvasRecorder.status !== RecorderStatus.Recording) return;
  await canvasRecorder.step();

  if (canvasRecorder.status !== RecorderStatus.Stopped) {
    requestAnimationFrame(() => tick());
  }
};

canvasRecorder = new Recorder(context, { name: "canvas-record-example" });

// Start and encode frame 0
await canvasRecorder.start();

// Animate to encode the rest
tick(canvasRecorder);

API

Encoder comparison:

Note:

• WebCodecs 5-10x faster than H264MP4Encoder and 20x faster than FFmpeg (it needs to mux files after writing png to virtual FS)
• FFmpeg (mp4 and webm) and WebCodecs (mp4) have a AVC maximum frame size of 9437184 pixels. That's fine until a bit more than 4K 16:9 @ 30fps. So if you need 4K Square or 8K exports, be patient with H264MP4Encoder (which probably also has the 4GB memory limit) or use Frame encoder and mux them manually with FFmpeg CLI.
• WebCodecs is embedded from mp4-wasm for ease of use (FFmpeg will require encoderOptions.corePath)

Roadmap:

• add debug logging
• use WebWorkers for gifenc

Modules

index

Re-export Recorder, RecorderStatus, all Encoders and utils.

Classes

Recorder

Base Recorder class.

Functions

onStatusChangeCb(RecorderStatus)

A callback to notify on the status change. To compare with RecorderStatus enum values.

Typedefs

RecorderOptions : Object

Options for recording. All optional.

RecorderStartOptions : Object

Options for recording. All optional.

index

Re-export Recorder, RecorderStatus, all Encoders and utils.

Recorder

Base Recorder class.

Kind: global class Properties

• Recorder
  • new Recorder(context, options)
  • .start(startOptions)
  • .step()
  • .stop()
  • .dispose()

new Recorder(context, options)

recorder.start(startOptions)

Start the recording by initializing and calling the initial step.

Kind: instance method of Recorder

recorder.step()

Encode a frame and increment the time and the playhead. Calls await canvasRecorder.stop() when duration is reached.

Kind: instance method of Recorder

recorder.stop()

Stop the recording and return the recorded buffer. If options.download is set, automatically start downloading the resulting file. Is called when duration is reached or manually.

Kind: instance method of Recorder

recorder.dispose()

Clean up

Kind: instance method of Recorder

RecorderStatus : enum

Enum for recorder status

Kind: global enum Read only: true Example

// Check recorder status before continuing
if (canvasRecorder.status !== RecorderStatus.Stopped) {
  rAFId = requestAnimationFrame(() => tick());
}

onStatusChangeCb(RecorderStatus)

A callback to notify on the status change. To compare with RecorderStatus enum values.

Kind: global function

RecorderOptions : Object

Options for recording. All optional.

Kind: global typedef Properties

RecorderStartOptions : Object

Options for recording. All optional.

Kind: global typedef Properties

License

All MIT:

• mp4-wasm
• h264-mp4-encoder
• @ffmpeg/ffmpeg
• gifenc
• webm-muxer

MIT. See license file.