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";
import { AVC } from "media-codecs";

// 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",
  encoderOptions: {
    codec: AVC.getCodec({ profile: "Main", level: "5.2" }),
  },
});

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

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

API

Encoder comparison:

Encoder	Extension	Required Web API	WASM	Speed
WebCodecs	mp4 / webm / mkv	WebCodecs	❌	Fast
MP4Wasm	mp4	WebCodecs	✅ (embed)	Fast
H264MP4	mp4		✅ (embed)	Medium
FFmpeg	mp4 / webm	SharedArrayBuffer	✅ (need binary path)	Slow
GIF	gif	WebWorkers (wip)	❌	Fast
Frame	png / jpg	File System Access	❌	Fast
MediaCapture	mkv / webm	MediaStream	❌	Realtime

Note:

• WebCodecs encoderOptions allow different codecs to be used: VP8/VP9/AV1/HEVC. See media-codecs to get a codec string from human readable options and check which ones are supported in your browser with github.io/media-codecs.
• 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 (ffmpeg -framerate 30 -i "%05d.jpg" -b:v 60M -r 30 -profile:v baseline -pix_fmt yuv420p -movflags +faststart output.mp4)
• MP4Wasm is embedded from mp4-wasm for ease of use (FFmpeg will require encoderOptions.corePath)

Roadmap:

• [ ] add debug logging
• [ ] use WebWorkers for gifenc

Modules

canvas-record

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

Classes

Recorder

Encoder

FFmpegEncoder

FrameEncoder

GIFEncoder

H264MP4Encoder

MediaCaptureEncoder

MP4WasmEncoder

WebCodecsEncoder

Constants

isWebCodecsSupported : boolean

Check for WebCodecs support on the current platform.

Functions

estimateBitRate(width, height, frameRate, motionRank, bitrateMode) ⇒ number

Estimate the bit rate of a video rounded to nearest megabit. Based on "H.264 for the rest of us" by Kush Amerasinghe.

Typedefs

onStatusChangeCb : function

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

RecorderOptions : object

Options for recording. All optional.

RecorderStartOptions : object

Options for recording initialisation. All optional.

EncoderExtensions : "mp4" | "webm" | "png" | "jpg" | "gif" | "mkv"

EncoderTarget : "in-browser" | "file-system"

FFmpegEncoderOptions : object

FFmpegEncoderEncoderOptions : module:@ffmpeg/ffmpeg/dist/esm/types.js~FFMessageLoadConfig

GIFEncoderOptions : object

GIFEncoderQuantizeOptions : object

GIFEncoderEncoderOptions : object

H264MP4EncoderOptions : object

H264MP4EncoderEncoderOptions : module:h264-mp4-encoder~H264MP4Encoder

MediaCaptureEncoderOptions : object

MediaCaptureEncoderEncoderOptions : MediaRecorderOptions

MP4WasmEncoderOptions : object

MP4WasmEncoderEncoderOptions : VideoEncoderConfig

WebCodecsEncoderOptions : object

WebCodecsEncoderEncoderOptions : VideoEncoderConfig

WebCodecsMuxerOptions : MuxerOptions

canvas-record

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

Recorder

Kind: global class

• Recorder
  • new Recorder(context, [options])
  • .defaultOptions : RecorderOptions
  • .mimeTypes : object
  • .start([startOptions])
  • .step()
  • .stop() ⇒ ArrayBuffer | Uint8Array | Array.<Blob> | undefined
  • .dispose()

new Recorder(context, [options])

Create a Recorder instance

Param	Type	Default
context	RenderingContext
[options]	RecorderOptions	{}

recorder.defaultOptions : RecorderOptions

Sensible defaults for recording so that the recorder "just works".

Kind: instance property of Recorder

recorder.mimeTypes : object

A mapping of extension to their mime types

Kind: instance property of Recorder

recorder.start([startOptions])

Start the recording by initializing and optionally calling the initial step.

Kind: instance method of Recorder

Param	Type	Default
[startOptions]	RecorderStartOptions	{}

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() ⇒ ArrayBuffer | Uint8Array | Array.<Blob> | undefined

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 the recorder and encoder

Kind: instance method of Recorder

Encoder

Kind: global class Properties

Name	Type
target	EncoderTarget
extension	EncoderExtensions
[encoderOptions]	object
[muxerOptions]	object

• Encoder
  • new Encoder(options)
  • .supportedExtensions : Array.<Extensions>
  • .supportedTargets : Array.<EncoderTarget>
  • .init(options)
  • .encode(frame, [frameNumber])
  • .stop() ⇒ ArrayBuffer | Uint8Array | Array.<Blob> | undefined
  • .dispose()

new Encoder(options)

Base Encoder class. All Encoders extend it and its method are called by the Recorder.

Param	Type
options	object

encoder.supportedExtensions : Array.<Extensions>

The extension the encoder supports

Kind: instance property of Encoder

encoder.supportedTargets : Array.<EncoderTarget>

The target to download the file to.

Kind: instance property of Encoder

encoder.init(options)

Setup the encoder: load binary, instantiate muxers, setup file system target...

Kind: instance method of Encoder

Param	Type
options	object

encoder.encode(frame, [frameNumber])

Encode a single frame. The frameNumber is usually used for GOP (Group Of Pictures).

Kind: instance method of Encoder

Param	Type
frame	number
[frameNumber]	number

encoder.stop() ⇒ ArrayBuffer | Uint8Array | Array.<Blob> | undefined

Stop the encoding process and cleanup the temporary data.

Kind: instance method of Encoder

encoder.dispose()

Clean up the encoder

Kind: instance method of Encoder

FFmpegEncoder

Kind: global class

new FFmpegEncoder([options])

Param	Type
[options]	FFmpegEncoderOptions

FrameEncoder

Kind: global class

GIFEncoder

Kind: global class

new GIFEncoder([options])

Param	Type
[options]	GIFEncoderOptions

H264MP4Encoder

Kind: global class

new H264MP4Encoder([options])

Param	Type
[options]	H264MP4EncoderOptions

MediaCaptureEncoder

Kind: global class

new MediaCaptureEncoder([options])

Param	Type
[options]	MediaCaptureEncoderOptions

MP4WasmEncoder

Kind: global class

new MP4WasmEncoder([options])

Param	Type
[options]	MP4WasmEncoderOptions

WebCodecsEncoder

Kind: global class

new WebCodecsEncoder([options])

Param	Type
[options]	WebCodecsEncoderOptions

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());
}

isWebCodecsSupported : boolean

Check for WebCodecs support on the current platform.

Kind: global constant

estimateBitRate(width, height, frameRate, motionRank, bitrateMode) ⇒ number

Estimate the bit rate of a video rounded to nearest megabit. Based on "H.264 for the rest of us" by Kush Amerasinghe.

Kind: global function Returns: number - A bitrate value in bits per second

Param	Type	Default	Description
width	number
height	number
frameRate	number	30
motionRank	number	4	A factor of 1, 2 or 4
bitrateMode	"variable" | "constant"	variable

Example

// Full HD (1080p)
const bitRate = estimateBitRate(1920, 1080, 30, "variable");
const bitRateMbps = bitRate * 1_000_000; // => 13 Mbps

onStatusChangeCb : function

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

Kind: global typedef

Param	Type	Description
RecorderStatus	number	the status

RecorderOptions : object

Options for recording. All optional.

Kind: global typedef Properties

Name	Type	Default	Description
[name]	string	"\"\""	A name for the recorder, used as prefix for the default file name.
[duration]	number	10	The recording duration in seconds. If set to Infinity, await canvasRecorder.stop() needs to be called manually.
[frameRate]	number	30	The frame rate in frame per seconds. Use await canvasRecorder.step(); to go to the next frame.
[download]	boolean	true	Automatically download the recording when duration is reached or when await canvasRecorder.stop() is manually called.
[extension]	string	"\"mp4\""	Default file extension: infers which Encoder is selected.
[target]	string	"\"in-browser\""	Default writing target: in-browser or file-system when available.
[encoder]	object		A specific encoder. Default encoder based on options.extension: GIF > WebCodecs > H264MP4.
[encoderOptions]	object		See src/encoders or individual packages for a list of options.
[muxerOptions]	object		See "mp4-muxer" and "webm-muxer" for a list of options.
[onStatusChange]	onStatusChangeCb

RecorderStartOptions : object

Options for recording initialisation. All optional.

Kind: global typedef Properties

Name	Type	Description
[filename]	string	Overwrite the file name completely.
[initOnly]	boolean	Only initialised the recorder and don't call the first await recorder.step().

EncoderExtensions : "mp4" | "webm" | "png" | "jpg" | "gif" | "mkv"

Kind: global typedef

EncoderTarget : "in-browser" | "file-system"

Kind: global typedef

FFmpegEncoderOptions : object

Kind: global typedef Properties

Name	Type	Default
[encoderOptions]	FFmpegEncoderEncoderOptions	{}

FFmpegEncoderEncoderOptions : code>module:@ffmpeg/ffmpeg/dist/esm/types.js~FFMessageLoadConfig</code

Kind: global typedef See: FFmpeg#load

GIFEncoderOptions : object

Kind: global typedef Properties

Name	Type	Default
[maxColors]	number	256
[quantizeOptions]	GIFEncoderQuantizeOptions
[encoderOptions]	GIFEncoderEncoderOptions	{}

GIFEncoderQuantizeOptions : object

Kind: global typedef See: QuantizeOptions Properties

Name	Type	Default
[format]	"rgb565" | "rgb444" | "rgba4444"	"rgb565"
[oneBitAlpha]	boolean | number	false
[clearAlpha]	boolean	true
[clearAlphaThreshold]	number	0
[clearAlphaColor]	number	0x00

GIFEncoderEncoderOptions : object

Kind: global typedef See: WriteFrameOpts Properties

Name	Type	Default
[palette]	Array.<Array.<number>>
[first]	boolean	false
[transparent]	boolean	0
[transparentIndex]	number	0
[delay]	number	0
[repeat]	number	0
[dispose]	number	-1

H264MP4EncoderOptions : object

Kind: global typedef Properties

Name	Type	Default
[debug]	boolean
[encoderOptions]	H264MP4EncoderEncoderOptions	{}

H264MP4EncoderEncoderOptions : module:h264-mp4-encoder~H264MP4Encoder

Kind: global typedef See: h264-mp4-encoder#api

MediaCaptureEncoderOptions : object

Kind: global typedef Properties

Name	Type	Default
[flushFrequency]	number	10
[encoderOptions]	MediaCaptureEncoderEncoderOptions	{}

MediaCaptureEncoderEncoderOptions : MediaRecorderOptions

Kind: global typedef See: MediaRecorder#options

MP4WasmEncoderOptions : object

Kind: global typedef Properties

Name	Type	Default
[groupOfPictures]	number	20
[flushFrequency]	number	10
[encoderOptions]	MP4WasmEncoderEncoderOptions	{}

MP4WasmEncoderEncoderOptions : VideoEncoderConfig

Kind: global typedef See: VideoEncoder.configure

WebCodecsEncoderOptions : object

Kind: global typedef Properties

Name	Type	Default
[groupOfPictures]	number	20
[flushFrequency]	number	10
[encoderOptions]	WebCodecsEncoderEncoderOptions	{}

WebCodecsEncoderEncoderOptions : VideoEncoderConfig

Kind: global typedef See: VideoEncoder.configure

WebCodecsMuxerOptions : MuxerOptions

Kind: global typedef See

• Mp4.MuxerOptions
• WebM.MuxerOptions

License

All MIT:

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

MIT. See license file.