local_sts.js

/**
 * Provides statistics for the local stream.
 */
var LocalStatsCollector = (function() {
    /**
     * Size of the webaudio analizer buffer.
     * @type {number}
     */
    var WEBAUDIO_ANALIZER_FFT_SIZE = 2048;

    /**
     * Value of the webaudio analizer smoothing time parameter.
     * @type {number}
     */
    var WEBAUDIO_ANALIZER_SMOOTING_TIME = 0.8;

    /**
     * <tt>LocalStatsCollector</tt> calculates statistics for the local stream.
     *
     * @param stream the local stream
     * @param interval stats refresh interval given in ms.
     * @param {function(LocalStatsCollector)} updateCallback the callback called on stats
     *                                   update.
     * @constructor
     */
    function LocalStatsCollectorProto(stream, interval, updateCallback) {
        window.AudioContext = window.AudioContext || window.webkitAudioContext;
        this.stream = stream;
        this.intervalId = null;
        this.intervalMilis = interval;
        this.audioLevelsUpdateCallback = updateCallback;
        this.audioLevel = 0;
    }

    /**
     * Starts the collecting the statistics.
     */
    LocalStatsCollectorProto.prototype.start = function () {
        if (!window.AudioContext)
            return;

        var context = new AudioContext();
        var analyser = context.createAnalyser();
        analyser.smoothingTimeConstant = WEBAUDIO_ANALIZER_SMOOTING_TIME;
        analyser.fftSize = WEBAUDIO_ANALIZER_FFT_SIZE;


        var source = context.createMediaStreamSource(this.stream);
        source.connect(analyser);


        var self = this;

        this.intervalId = setInterval(
            function () {
                var array = new Uint8Array(analyser.frequencyBinCount);
                analyser.getByteTimeDomainData(array);
                var audioLevel = TimeDomainDataToAudioLevel(array);
                if(audioLevel != self.audioLevel) {
                    self.audioLevel = animateLevel(audioLevel, self.audioLevel);
                    self.audioLevelsUpdateCallback(LocalStatsCollectorProto.LOCAL_JID, self.audioLevel);
                }
            },
            this.intervalMilis
        );

    };

    /**
     * Stops collecting the statistics.
     */
    LocalStatsCollectorProto.prototype.stop = function () {
        if (this.intervalId) {
            clearInterval(this.intervalId);
            this.intervalId = null;
        }
    };

    /**
     * Converts time domain data array to audio level.
     * @param array the time domain data array.
     * @returns {number} the audio level
     */
    var TimeDomainDataToAudioLevel = function (samples) {

        var maxVolume = 0;

        var length = samples.length;

        for (var i = 0; i < length; i++) {
            if (maxVolume < samples[i])
                maxVolume = samples[i];
        }

        return parseFloat(((maxVolume - 127) / 128).toFixed(3));
    };

    /**
     * Animates audio level change
     * @param newLevel the new audio level
     * @param lastLevel the last audio level
     * @returns {Number} the audio level to be set
     */
    function animateLevel(newLevel, lastLevel)
    {
        var value = 0;
        var diff = lastLevel - newLevel;
        if(diff > 0.2)
        {
            value = lastLevel - 0.2;
        }
        else if(diff < -0.4)
        {
            value = lastLevel + 0.4;
        }
        else
        {
            value = newLevel;
        }

        return parseFloat(value.toFixed(3));
    }

    /**
     * Indicates that this audio level is for local jid.
     * @type {string}
     */
    LocalStatsCollectorProto.LOCAL_JID = 'local';

    return LocalStatsCollectorProto;
})();