guacamole-client/guacamole-common-js/src/main/webapp/modules/AudioChannel.js

/*
 * Copyright (C) 2013 Glyptodon LLC
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

var Guacamole = Guacamole || {};

/**
 * Abstract audio channel which queues and plays arbitrary audio data.
 * @constructor
 */
Guacamole.AudioChannel = function() {

    /**
     * Reference to this AudioChannel.
     * @private
     */
    var channel = this;

    /**
     * When the next packet should play.
     * @private
     */
    var next_packet_time = 0;

    /**
     * Queues up the given data for playing by this channel once all previously
     * queued data has been played. If no data has been queued, the data will
     * play immediately.
     * 
     * @param {String} mimetype The mimetype of the data provided.
     * @param {Number} duration The duration of the data provided, in
     *                          milliseconds.
     * @param {Blob} data The blob data to play.
     */
    this.play = function(mimetype, duration, data) {

        var packet =
            new Guacamole.AudioChannel.Packet(mimetype, data);

        var now = Guacamole.AudioChannel.getTimestamp();

        // If underflow is detected, reschedule new packets relative to now.
        if (next_packet_time < now)
            next_packet_time = now;

        // Schedule next packet
        packet.play(next_packet_time);
        next_packet_time += duration;

    };

};

// Define context if available
if (window.webkitAudioContext) {
    Guacamole.AudioChannel.context = new webkitAudioContext();
}

/**
 * Returns a base timestamp which can be used for scheduling future audio
 * playback. Scheduling playback for the value returned by this function plus
 * N will cause the associated audio to be played back N milliseconds after
 * the function is called.
 *
 * @return {Number} An arbitrary channel-relative timestamp, in milliseconds.
 */
Guacamole.AudioChannel.getTimestamp = function() {

    // If we have an audio context, use its timestamp
    if (Guacamole.AudioChannel.context)
        return Guacamole.AudioChannel.context.currentTime * 1000;

    // If we have high-resolution timers, use those
    if (window.performance) {

        if (window.performance.now)
            return window.performance.now();

        if (window.performance.webkitNow)
            return window.performance.webkitNow();
        
    }

    // Fallback to millisecond-resolution system time
    return new Date().getTime();

};

/**
 * Abstract representation of an audio packet.
 * 
 * @constructor
 * 
 * @param {String} mimetype The mimetype of the data contained by this packet.
 * @param {Blob} data The blob of sound data contained by this packet.
 */
Guacamole.AudioChannel.Packet = function(mimetype, data) {

    /**
     * Schedules this packet for playback at the given time.
     *
     * @function
     * @param {Number} when The time this packet should be played, in
     *                      milliseconds.
     */
    this.play = undefined; // Defined conditionally depending on support

    // If audio API available, use it.
    if (Guacamole.AudioChannel.context) {

        var readyBuffer = null;

        // By default, when decoding finishes, store buffer for future
        // playback
        var handleReady = function(buffer) {
            readyBuffer = buffer;
        };

        // Read data and start decoding
        var reader = new FileReader();
        reader.onload = function() {
            Guacamole.AudioChannel.context.decodeAudioData(
                reader.result,
                function(buffer) { handleReady(buffer); }
            );
        };
        reader.readAsArrayBuffer(data);

        // Set up buffer source
        var source = Guacamole.AudioChannel.context.createBufferSource();
        source.connect(Guacamole.AudioChannel.context.destination);

        // Use noteOn() instead of start() if necessary
        if (!source.start)
            source.start = source.noteOn;

        var play_when;

        function playDelayed(buffer) {
            source.buffer = buffer;
            source.start(play_when / 1000);
        }

        /** @ignore */
        this.play = function(when) {
            
            play_when = when;
            
            // If buffer available, play it NOW
            if (readyBuffer)
                playDelayed(readyBuffer);

            // Otherwise, play when decoded
            else
                handleReady = playDelayed;

        };

    }

    else {

        var play_on_load = false;

        // Create audio element to house and play the data
        var audio = new Audio();

        // Read data and start decoding
        var reader = new FileReader();
        reader.onload = function() {

            var binary = "";
            var bytes = new Uint8Array(reader.result);

            // Produce binary string from bytes in buffer
            for (var i=0; i<bytes.byteLength; i++)
                binary += String.fromCharCode(bytes[i]);

            // Convert to data URI 
            audio.src = "data:" + mimetype + ";base64," + window.btoa(binary);

            // Play if play was attempted but packet wasn't loaded yet
            if (play_on_load)
                audio.play();

        };
        reader.readAsArrayBuffer(data);
   
        function play() {

            // If audio data is ready, play now
            if (audio.src)
                audio.play();

            // Otherwise, play when loaded
            else
                play_on_load = true;

        }
        
        /** @ignore */
        this.play = function(when) {
            
            // Calculate time until play
            var now = Guacamole.AudioChannel.getTimestamp();
            var delay = when - now;
            
            // Play now if too late
            if (delay < 0)
                play();

            // Otherwise, schedule later playback
            else
                window.setTimeout(play, delay);

        };

    }

};