ImageCapture polyfill
ImageCapture is a polyfill for the MediaStream Image Capture API.
Status
As of June 2017, the ImageCapture spec is relatively stable. Chrome supports the API starting with M59 (earlier versions require setting a flag) and Firefox has partial support behind a flag. See the ImageCapture browser support page for details.
Prior art
Prior to this API, in order to take a still picture from the device camera, two approaches have been used:
- Set the source of a
<video>
element to a stream obtained via navigator[.mediaDevices].getUserMedia
, then use a 2D canvas context to drawImage
from that video. The canvas
can return a URL to be used as the src
attribute of an <img>
element, via .toDataURL('image/<format>')
. (1, 2) - Use the HTML Media Capture API, i.e.
<input type="file" name="image" accept="image/*" capture>
Demo
The demo currently shows grabFrame() and takePhoto().
Quick start
yarn add image-capture
Or, with npm:
npm install --save image-capture
In your JS code:
let videoDevice;
let canvas = document.getElementById('canvas');
let photo = document.getElementById('photo');
navigator.mediaDevices.getUserMedia({video: true}).then(gotMedia).catch(failedToGetMedia);
function gotMedia(mediaStream) {
videoDevice = mediaStream.getVideoTracks()[0];
let captureDevice = new ImageCapture(videoDevice);
if (captureDevice) {
captureDevice.takePhoto().then(processPhoto).catch(stopCamera);
captureDevice.grabFrame().then(processFrame).catch(stopCamera);
}
}
function processPhoto(blob) {
photo.src = window.URL.createObjectURL(blob);
}
function processFrame(imageBitmap) {
canvas.width = imageBitmap.width;
canvas.height = imageBitmap.height;
canvas.getContext('2d').drawImage(imageBitmap, 0, 0);
}
function stopCamera(error) {
console.error(error);
if (videoDevice) videoDevice.stop();
}
photo.addEventListener('load', function () {
window.URL.revokeObjectURL(this.src);
});
Methods
Start by constructing a new ImageCapture object:
let captureDevice;
navigator.mediaDevices.getUserMedia({video: true}).then(mediaStream => {
captureDevice = new ImageCapture(mediaStream.getVideoTracks()[0]);
}).catch(...)
Please consult the spec for full detail on the methods.
constructor(videoStreamTrack)
Takes a video track and returns an ImageCapture object.
getPhotoCapabilities
TBD
setOptions
TBD
takePhoto
Capture the video stream into a Blob containing a single still image.
Returns a Promise that resolves to a Blob on success, or is rejected with DOMException
on failure.
captureDevice.takePhoto().then(blob => {
}).catch(error => ...);
grabFrame
Gather data from the video stream into an ImageBitmap object. The width and height of the ImageBitmap object are derived from the constraints of the video stream track passed to the constructor.
Returns a Promise that resolves to an ImageBitmap on success, or is rejected with DOMException
on failure.
captureDevice.grabFrame().then(imageBitmap => {
}).catch(error => ...);
Compatibility
The polyfill has been tested to work in current browsers:
- Chrome 55+
- Firefox 49+
- Chrome 52+ for Android
- Firefox 48+ for Android
For the widest compatibility, you can additionally load the WebRTC adapter. That will expand support to:
For older browsers that don't support navigator.getUserMedia, you can additionally load Addy Osmani's shim with optional fallback to Flash - getUserMedia.js. Alternatively, the getUserMedia wrapper normalizes error handling and gives an error-first API with cross-browser support.
Development
yarn
yarn run dev
npm
npm install
npm run dev
To make your server accessible outside of localhost
, run npm/yarn run lt
.
Before committing, make sure you pass yarn/npm run lint
without errors, and run yarn/npm run docs
to generate the demo.