quaggaJS/src/camera_access.js

/* jshint undef: true, unused: true, browser:true, devel: true */
/* global define, MediaStreamTrack */

define(["html_utils"], function(HtmlUtils) {
    "use strict";
    var streamRef,
        loadedDataHandler;

    /**
     * Wraps browser-specific getUserMedia
     * @param {Object} constraints
     * @param {Object} success Callback
     * @param {Object} failure Callback
     */
    function getUserMedia(constraints, success, failure) {
        if (typeof navigator.getUserMedia !== 'undefined') {
            navigator.getUserMedia(constraints, function (stream) {
                streamRef = stream;
                var videoSrc = (window.URL && window.URL.createObjectURL(stream)) || stream;
                success.apply(null, [videoSrc]);
            }, failure);
        } else {
            failure(new TypeError("getUserMedia not available"));
        }
    }

    function loadedData(video, callback) {
        var attempts = 10;

        function checkVideo() {
            if (attempts > 0) {
                if (video.videoWidth > 0 && video.videoHeight > 0) {
                    console.log(video.videoWidth + "px x " + video.videoHeight + "px");
                    callback();
                } else {
                    window.setTimeout(checkVideo, 500);
                }
            } else {
                callback('Unable to play video stream. Is webcam working?');
            }
            attempts--;
        }
        checkVideo();
    }

    /**
     * Tries to attach the camera-stream to a given video-element
     * and calls the callback function when the content is ready
     * @param {Object} constraints
     * @param {Object} video
     * @param {Object} callback
     */
    function initCamera(constraints, video, callback) {
        getUserMedia(constraints, function(src) {
            video.src = src;
            if (loadedDataHandler) {
                video.removeEventListener("loadeddata", loadedDataHandler, false);
            }
            loadedDataHandler = loadedData.bind(null, video, callback);
            video.addEventListener('loadeddata', loadedDataHandler, false);
            video.play();
        }, function(e) {
            callback(e);
        });
    }

    /**
     * Normalizes the incoming constraints to satisfy the current browser
     * @param config
     * @param cb Callback which is called whenever constraints are created
     * @returns {*}
     */
    function normalizeConstraints(config, cb) {
        var constraints = {
                audio: false,
                video: true
            },
            videoConstraints = HtmlUtils.mergeObjects({
                width: 640,
                height: 480,
                minAspectRatio: 0,
                maxAspectRatio: 100,
                facing: "environment"
            }, config);

        if ( typeof MediaStreamTrack !== 'undefined' && typeof MediaStreamTrack.getSources !== 'undefined') {
            MediaStreamTrack.getSources(function(sourceInfos) {
                var videoSourceId;
                for (var i = 0; i != sourceInfos.length; ++i) {
                    var sourceInfo = sourceInfos[i];
                    if (sourceInfo.kind == "video" && sourceInfo.facing == videoConstraints.facing) {
                        videoSourceId = sourceInfo.id;
                    }
                }
                constraints.video = {
                    mandatory: {
                        minWidth: videoConstraints.width,
                        minHeight: videoConstraints.height,
                        minAspectRatio: videoConstraints.minAspectRatio,
                        maxAspectRatio: videoConstraints.maxAspectRatio
                    },
                    optional: [{
                        sourceId: videoSourceId
                    }]
                };
                return cb(constraints);
            });
        } else {
            constraints.video = {
                mediaSource: "camera",
                width: { min: videoConstraints.width, max: videoConstraints.width },
                height: { min: videoConstraints.height, max: videoConstraints.height },
                require: ["width", "height"]
            };
            return cb(constraints);
        }
    }

    /**
     * Requests the back-facing camera of the user. The callback is called
     * whenever the stream is ready to be consumed, or if an error occures.
     * @param {Object} video
     * @param {Object} callback
     */
    function request(video, videoConstraints, callback) {
        normalizeConstraints(videoConstraints, function(constraints) {
            initCamera(constraints, video, callback);
        });
    }

    return {
        request : function(video, constraints, callback) {
            request(video, constraints, callback);
        },
        release : function() {
            var tracks = streamRef && streamRef.getVideoTracks();
            if (tracks.length) {
                tracks[0].stop();
            }
            streamRef = null;
        }
    };
});