canvas-record


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



Installation

``bash
npm install canvas-record
`

Usage

`js
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 / mov | 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" | "mov"

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 : module:mediabunny~OutputOptions

canvas-record

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

Recorder

Kind: global class

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

$3

Create a Recorder instance

| Param | Type | Default |
| --------- | ------------------------------------------------ | --------------- |
| context | RenderingContext | |
| [options] | RecorderOptions | {} |

$3

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

Kind: instance property of Recorder


$3

A mapping of extension to their mime types

Kind: instance property of Recorder


$3

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

Kind: instance method of Recorder

| Param | Type | Default |
| -------------- | ---------------------------------------------------------- | --------------- |
| [startOptions] | RecorderStartOptions | {} |

$3

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

Kind: instance method of Recorder


$3

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


$3

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])](#Encoder+encode)
- .stop() ⇒ ArrayBuffer \| Uint8Array \| Array.<Blob> \| undefined
- .dispose()

$3

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

| Param | Type |
| ------- | ------------------- |
| options | object |

$3

The extension the encoder supports

Kind: instance property of Encoder


$3

The target to download the file to.

Kind: instance property of Encoder


$3

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

Kind: instance method of Encoder

| Param | Type |
| ------- | ------------------- |
| options | object |

$3

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 |

$3

Stop the encoding process and cleanup the temporary data.

Kind: instance method of Encoder


$3

Clean up the encoder

Kind: instance method of Encoder


FFmpegEncoder

Kind: global class


$3

| Param | Type |
| --------- | ---------------------------------------------------------- |
| [options] | FFmpegEncoderOptions |

FrameEncoder

Kind: global class


GIFEncoder

Kind: global class


$3

| Param | Type |
| --------- | ---------------------------------------------------- |
| [options] | GIFEncoderOptions |

H264MP4Encoder

Kind: global class


$3

| Param | Type |
| --------- | ------------------------------------------------------------ |
| [options] | H264MP4EncoderOptions |

MediaCaptureEncoder

Kind: global class


$3

| Param | Type |
| --------- | ---------------------------------------------------------------------- |
| [options] | MediaCaptureEncoderOptions |

MP4WasmEncoder

Kind: global class


$3

| Param | Type |
| --------- | ------------------------------------------------------------ |
| [options] | MP4WasmEncoderOptions |

WebCodecsEncoder

Kind: global class


$3

| Param | Type |
| --------- | ---------------------------------------------------------------- |
| [options] | WebCodecsEncoderOptions |

RecorderStatus : enum

Enum for recorder status

Kind: global enum
Read only: true
Example

`js
// 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

`js
// 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. |
| [rect] | Array | [] | Sub-region [x, y, width, height] of the canvas to encode from bottom left. Default to 0, 0 and context.drawingBufferWidth/drawingBufferHeight or canvas.width/height. |
| [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 "mediabunny" for a list of options. |
| [frameOptions] | object | | Options for createImageBitmap(), VideoFrame, getImageData() or canvas-screenshot. |
| [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" \| "mov"

Kind: global typedef

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

Kind: global typedef

FFmpegEncoderOptions : object

Kind: global typedef
Properties

| Name | Type | Default |
| ---------------- | ------------------------------------------------------------------------ | --------------- |
| [encoderOptions] | FFmpegEncoderEncoderOptions | {} |

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

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 : module:mediabunny~OutputOptions

Kind: global typedef
See: mediabunny#output-formats

License

All MIT:

- mp4-wasm
- h264-mp4-encoder
- @ffmpeg/ffmpeg
- gifenc
- mediabunny

MIT. See license file.