decodeFromConstraints(constraints, videoSource, callbackFn) {
			return __awaiter(this, void 0, void 0, function* () {
				const stream = yield navigator.mediaDevices.getUserMedia(constraints);
				return yield this.decodeFromStream(stream, videoSource, callbackFn);
			});
		}
Continuously tries to decode the barcode from a stream obtained from the given constraints while showing the video in the specified video element.

@param {MediaStream} [constraints] the media stream constraints to get s valid media stream to decode from
@param {string|HTMLVideoElement} [video] the video element in page where to show the video while decoding. Can be either an element id or directly an HTMLVideoElement. Can be undefined, in which case no video will be shown.
@returns {Promise<Result>} The decoding result.

@memberOf BrowserCodeReader