midi.js

/*jslint es5: true, laxbreak: true */

(function (window) {

var AP = Array.prototype;

// Create a mock console object to void undefined errors if the console object
// is not defined.
if (!window.console || !console.firebug) {
    var names = ["log", "debug", "info", "warn", "error"];

    window.console = {};
    for (var i = 0; i < names.length; ++i) {
        window.console[names[i]] = function() {};
    }
}

var DEFAULT_VOLUME   = 90;
var DEFAULT_DURATION = 128;
var DEFAULT_CHANNEL  = 0;

// These are the different values that compose a MID header. They are already
// expressed in their string form, so no useless conversion has to take place
// since they are constants.

var HDR_CHUNKID     = "MThd";
var HDR_CHUNK_SIZE  = "\x00\x00\x00\x06"; // Header size for SMF
var HDR_TYPE0       = "\x00\x00"; // Midi Type 0 id
var HDR_TYPE1       = "\x00\x01"; // Midi Type 1 id
var HDR_SPEED       = "\x00\x80"; // Defaults to 128 ticks per beat

// Midi event codes
var EVT_NOTE_OFF           = 0x8;
var EVT_NOTE_ON            = 0x9;
var EVT_AFTER_TOUCH        = 0xA;
var EVT_CONTROLLER         = 0xB;
var EVT_PROGRAM_CHANGE     = 0xC;
var EVT_CHANNEL_AFTERTOUCH = 0xD;
var EVT_PITCH_BEND         = 0xE;

var META_SEQUENCE   = 0x00;
var META_TEXT       = 0x01;
var META_COPYRIGHT  = 0x02;
var META_TRACK_NAME = 0x03;
var META_INSTRUMENT = 0x04;
var META_LYRIC      = 0x05;
var META_MARKER     = 0x06;
var META_CUE_POINT  = 0x07;
var META_CHANNEL_PREFIX = 0x20;
var META_END_OF_TRACK   = 0x2f;
var META_TEMPO      = 0x51;
var META_SMPTE      = 0x54;
var META_TIME_SIG   = 0x58;
var META_KEY_SIG    = 0x59;
var META_SEQ_EVENT  = 0x7f;

// This is the conversion table from notes to its MIDI number. Provided for
// convenience, it is not used in this code.
var noteTable = { "G9": 0x7F, "Gb9": 0x7E, "F9": 0x7D, "E9": 0x7C, "Eb9": 0x7B,
"D9": 0x7A, "Db9": 0x79, "C9": 0x78, "B8": 0x77, "Bb8": 0x76, "A8": 0x75, "Ab8": 0x74,
"G8": 0x73, "Gb8": 0x72, "F8": 0x71, "E8": 0x70, "Eb8": 0x6F, "D8": 0x6E, "Db8": 0x6D,
"C8": 0x6C, "B7": 0x6B, "Bb7": 0x6A, "A7": 0x69, "Ab7": 0x68, "G7": 0x67, "Gb7": 0x66,
"F7": 0x65, "E7": 0x64, "Eb7": 0x63, "D7": 0x62, "Db7": 0x61, "C7": 0x60, "B6": 0x5F,
"Bb6": 0x5E, "A6": 0x5D, "Ab6": 0x5C, "G6": 0x5B, "Gb6": 0x5A, "F6": 0x59, "E6": 0x58,
"Eb6": 0x57, "D6": 0x56, "Db6": 0x55, "C6": 0x54, "B5": 0x53, "Bb5": 0x52, "A5": 0x51,
"Ab5": 0x50, "G5": 0x4F, "Gb5": 0x4E, "F5": 0x4D, "E5": 0x4C, "Eb5": 0x4B, "D5": 0x4A,
"Db5": 0x49, "C5": 0x48, "B4": 0x47, "Bb4": 0x46, "A4": 0x45, "Ab4": 0x44, "G4": 0x43,
"Gb4": 0x42, "F4": 0x41, "E4": 0x40, "Eb4": 0x3F, "D4": 0x3E, "Db4": 0x3D, "C4": 0x3C,
"B3": 0x3B, "Bb3": 0x3A, "A3": 0x39, "Ab3": 0x38, "G3": 0x37, "Gb3": 0x36, "F3": 0x35,
"E3": 0x34, "Eb3": 0x33, "D3": 0x32, "Db3": 0x31, "C3": 0x30, "B2": 0x2F, "Bb2": 0x2E,
"A2": 0x2D, "Ab2": 0x2C, "G2": 0x2B, "Gb2": 0x2A, "F2": 0x29, "E2": 0x28, "Eb2": 0x27,
"D2": 0x26, "Db2": 0x25, "C2": 0x24, "B1": 0x23, "Bb1": 0x22, "A1": 0x21, "Ab1": 0x20,
"G1": 0x1F, "Gb1": 0x1E, "F1": 0x1D, "E1": 0x1C, "Eb1": 0x1B, "D1": 0x1A, "Db1": 0x19,
"C1": 0x18, "B0": 0x17, "Bb0": 0x16, "A0": 0x15, "Ab0": 0x14, "G0": 0x13, "Gb0": 0x12,
"F0": 0x11, "E0": 0x10, "Eb0": 0x0F, "D0": 0x0E, "Db0": 0x0D, "C0": 0x0C };

// Helper functions

/*
 * Converts a string into an array of ASCII char codes for every character of
 * the string.
 *
 * @param str {String} String to be converted
 * @returns array with the charcode values of the string
 */
function StringToNumArray(str) {
    return AP.map.call(str, function(char) {
        return char.charCodeAt(0);
    });
}

/*
 * Converts an array of bytes to a string of hexadecimal characters. Prepares
 * it to be converted into a base64 string.
 *
 * @param byteArray {Array} array of bytes that will be converted to a string
 * @returns hexadecimal string
 */
function codes2Str(byteArray) {
    return String.fromCharCode.apply(null, byteArray);
}

/*
 * Converts a String of hexadecimal values to an array of bytes. It can also
 * add remaining "0" nibbles in order to have enough bytes in the array as the
 * |finalBytes| parameter.
 *
 * @param str {String} string of hexadecimal values e.g. "097B8A"
 * @param finalBytes {Integer} Optional. The desired number of bytes that the returned array should contain
 * @returns array of nibbles.
 */

function str2Bytes(str, finalBytes) {
    if (finalBytes) {
        while ((str.length / 2) < finalBytes) { str = "0" + str; }
    }

    var bytes = [];
    for (var i=str.length-1; i>=0; i = i-2) {
        var chars = i === 0 ? str[i] : str[i-1] + str[i];
        bytes.unshift(parseInt(chars, 16));
    }

    return bytes;
}

function isArray(obj) {
    return !!(obj && obj.concat && obj.unshift && !obj.callee);
}


/**
 * Translates number of ticks to MIDI timestamp format, returning an array of
 * bytes with the time values. Midi has a very particular time to express time,
 * take a good look at the spec before ever touching this function.
 *
 * @param ticks {Integer} Number of ticks to be translated
 * @returns Array of bytes that form the MIDI time value
 */
var translateTickTime = function(ticks) {
    var buffer = ticks & 0x7F;

    while (ticks = ticks >> 7) {
        buffer <<= 8;
        buffer |= ((ticks & 0x7F) | 0x80);
    }

    var bList = [];
    while (true) {
        bList.push(buffer & 0xff);

        if (buffer & 0x80) { buffer >>= 8; }
        else { break; }
    }
    return bList;
};

/*
 * This is the function that assembles the MIDI file. It writes the
 * necessary constants for the MIDI header and goes through all the tracks, appending
 * their data to the final MIDI stream.
 * It returns an object with the final values in hex and in base64, and with
 * some useful methods to play an manipulate the resulting MIDI stream.
 *
 * @param config {Object} Configuration object. It contains the tracks, tempo
 * and other values necessary to generate the MIDI stream.
 *
 * @returns An object with the hex and base64 resulting streams, as well as
 * with some useful methods.
 */
var MidiWriter = function(config) {
    if (config) {
        var tracks  = config.tracks || [];
        // Number of tracks in hexadecimal
        var tracksLength = tracks.length.toString(16);

        // This variable will hold the whole midi stream and we will add every
        // chunk of MIDI data to it in the next lines.
        var hexMidi = HDR_CHUNKID + HDR_CHUNK_SIZE + HDR_TYPE0;

        // Appends the number of tracks expressed in 2 bytes, as the MIDI
        // standard requires.
        hexMidi += codes2Str(str2Bytes(tracksLength, 2));
        hexMidi += HDR_SPEED;
        // Goes through the tracks appending the hex strings that compose them.
        tracks.forEach(function(trk) { hexMidi += codes2Str(trk.toBytes()); });

        return {
            b64: btoa(hexMidi),
            play: function() {
                if (document) {
                    var embed = document.createElement("embed");
                    embed.setAttribute("src", "data:audio/midi;base64," + this.b64);
                    embed.setAttribute("type", "audio/midi");
                    document.body.appendChild(embed);
                }
            },
            save: function() {
                window.open("data:audio/midi;base64," + this.b64,
                            "JSMidi generated output",
                            "resizable=yes,scrollbars=no,status=no");
            }
        };

    } else {
        throw new Error("No parameters have been passed to MidiWriter.");
    }
};

/*
 * Generic MidiEvent object. This object is used to create standard MIDI events
 * (note Meta events nor SysEx events). It is passed a |params| object that may
 * contain the keys time, type, channel, param1 and param2. Note that only the
 * type, channel and param1 are strictly required. If the time is not provided,
 * a time of 0 will be assumed.
 *
 * @param {object} params Object containing the properties of the event.
 */
var MidiEvent = function(params) {
    if (params &&
        (params.type    !== null || params.type    !== undefined) &&
        (params.channel !== null || params.channel !== undefined) &&
        (params.param1  !== null || params.param1  !== undefined)) {
        this.setTime(params.time);
        this.setType(params.type);
        this.setChannel(params.channel);
        this.setParam1(params.param1);
        this.setParam2(params.param2);
    } else {
        throw new Error("Not enough parameters to create an event.");
    }
};


/**
 * Returns the list of events that form a note in MIDI. If the |sustained|
 * parameter is not specified, it creates the noteOff event, which stops the
 * note after it has been played, instead of keeping it playing.
 *
 * This method accepts two ways of expressing notes. The first one is a string,
 * which will be looked up in the global |noteTable| but it will take the
 * default values for pitch, channel, durtion and volume.
 *
 * If a note object is passed to the method instead, it should contain the properties
 * channel, pitch, duration and volume, of which pitch is mandatory. In case the
 * channel, the duration or the volume are not passed, default values will be
 * used.
 *
 * @param note {object || String} Object with note properties or string
 * @param sustained {Boolean} Whether the note has to end or keep playing
 * @returns Array of events, with a maximum of two events (noteOn and noteOff)
 */

MidiEvent.createNote = function(note, sustained) {
    if (!note) { throw new Error("Note not specified"); }

    if (typeof note === "string") {
        note = noteTable[note];
    // The pitch is mandatory if the note object is used.
    } else if (!note.pitch) {
        throw new Error("The pitch is required in order to create a note.");
    }

    var events = [];
    events.push(MidiEvent.noteOn(note));

    // If there is a |sustained| parameter, the note will keep playing until
    // a noteOff event is issued for it.
    if (!sustained) {
        // The noteOff event will be the one that is passed the actual duration
        // value for the note, since it is the one that will stop playing the
        // note at a particular time. If not specified it takes the default
        // value for it.
        // TODO: Is is good to have a default value for it?
        events.push(MidiEvent.noteOff(note, note.duration || DEFAULT_DURATION));
    }

    return events;
};

/**
 * Returns an event of the type NOTE_ON taking the values passed and falling
 * back to defaults if they are not specified.
 *
 * @param note {Note || String} Note object or string
 * @param time {Number} Duration of the note in ticks
 * @returns MIDI event with type NOTE_ON for the note specified
 */
MidiEvent.noteOn = function(note, duration) {
    return new MidiEvent({
        time:    note.duration || duration || 0,
        type:    EVT_NOTE_ON,
        channel: note.channel || DEFAULT_CHANNEL,
        param1:  note.pitch   || note,
        param2:  note.volume  || DEFAULT_VOLUME
    });
};

/**
 * Returns an event of the type NOTE_OFF taking the values passed and falling
 * back to defaults if they are not specified.
 *
 * @param note {Note || String} Note object or string
 * @param time {Number} Duration of the note in ticks
 * @returns MIDI event with type NOTE_OFF for the note specified
 */

MidiEvent.noteOff = function(note, duration) {
    return new MidiEvent({
        time:    note.duration || duration || 0,
        type:    EVT_NOTE_OFF,
        channel: note.channel || DEFAULT_CHANNEL,
        param1:  note.pitch   || note,
        param2:  note.volume  || DEFAULT_VOLUME
    });
};


MidiEvent.prototype = {
    type: 0,
    channel: 0,
    time: 0,
    setTime: function(ticks) {
        // The 0x00 byte is always the last one. This is how Midi
        // interpreters know that the time measure specification ends and the
        // rest of the event signature starts.

        this.time = translateTickTime(ticks || 0);
    },
    setType: function(type) {
        if (type < EVT_NOTE_OFF || type > EVT_PITCH_BEND) {
            throw new Error("Trying to set an unknown event: " + type);
        }

        this.type = type;
    },
    setChannel: function(channel) {
        if (channel < 0 || channel > 15) {
            throw new Error("Channel is out of bounds.");
        }

        this.channel = channel;
    },
    setParam1: function(p) {
        this.param1 = p;
    },
    setParam2: function(p) {
        this.param2 = p;
    },
    toBytes: function() {
        var byteArray = [];

        var typeChannelByte =
            parseInt(this.type.toString(16) + this.channel.toString(16), 16);

        byteArray.push.apply(byteArray, this.time);
        byteArray.push(typeChannelByte);
        byteArray.push(this.param1);

        // Some events don't have a second parameter
        if (this.param2 !== undefined && this.param2 !== null) {
            byteArray.push(this.param2);
        }
        return byteArray;
    }
};

var MetaEvent = function(params) {
    if (params) {
        this.setType(params.type);
        this.setData(params.data);
    }
};

MetaEvent.prototype = {
    setType: function(t) {
        this.type = t;
    },
    setData: function(d) {
        this.data = d;
    },
    toBytes: function() {
        if (!this.type || !this.data) {
            throw new Error("Type or data for meta-event not specified.");
        }

        var byteArray = [0xff, this.type];

        // If data is an array, we assume that it contains several bytes. We
        // apend them to byteArray.
        if (isArray(this.data)) {
            AP.push.apply(byteArray, this.data);
        }

        return byteArray;
    }
};

var MidiTrack = function(cfg) {
    this.events = [];
    for (var p in cfg) {
        if (cfg.hasOwnProperty(p)) {
            // Get the setter for the property. The property is capitalized.
            // Probably a try/catch should go here.
            this["set" + p.charAt(0).toUpperCase() + p.substring(1)](cfg[p]);
        }
    }
};

//"MTrk" Marks the start of the track data
MidiTrack.TRACK_START = [0x4d, 0x54, 0x72, 0x6b];
MidiTrack.TRACK_END   = [0x0, 0xFF, 0x2F, 0x0];

MidiTrack.prototype = {
    /*
     * Adds an event to the track.
     *
     * @param event {MidiEvent} Event to add to the track
     * @returns the track where the event has been added
     */
    addEvent: function(event) {
        this.events.push(event);
        return this;
    },
    setEvents: function(events) {
        AP.push.apply(this.events, events);
        return this;
    },
    /*
     * Adds a text meta-event to the track.
     *
     * @param type {Number} type of the text meta-event
     * @param text {String} Optional. Text of the meta-event.
     * @returns the track where the event ahs been added
     */
    setText: function(type, text) {
        // If the param text is not specified, it is assumed that a generic
        // text is wanted and that the type parameter is the actual text to be
        // used.
        if (!text) {
            type = META_TEXT;
            text = type;
        }
        return this.addEvent(new MetaEvent({ type: type, data: text }));
    },
    // The following are setters for different kinds of text in MIDI, they all
    // use the |setText| method as a proxy.
    setCopyright:  function(text) { return this.setText(META_COPYRIGHT, text);  },
    setTrackName:  function(text) { return this.setText(META_TRACK_NAME, text); },
    setInstrument: function(text) { return this.setText(META_INSTRUMENT, text); },
    setLyric:      function(text) { return this.setText(META_LYRIC, text);      },
    setMarker:     function(text) { return this.setText(META_MARKER, text);     },
    setCuePoint:   function(text) { return this.setText(META_CUE_POINT, text);  },

    setTempo: function(tempo) {
        this.addEvent(new MetaEvent({ type: META_TEMPO, data: tempo }));
    },
    setTimeSig: function() {
        // TBD
    },
    setKeySig: function() {
        // TBD
    },

    toBytes: function() {
        var trackLength = 0;
        var eventBytes = [];
        var startBytes = MidiTrack.TRACK_START;
        var endBytes   = MidiTrack.TRACK_END;

        /*
         * Adds the bytes of an event to the eventBytes array and add the
         * amount of bytes to |trackLength|.
         *
         * @param event {MidiEvent} MIDI event we want the bytes from.
         */
        var addEventBytes = function(event) {
            var bytes = event.toBytes();
            trackLength += bytes.length;
            AP.push.apply(eventBytes, bytes);
        };

        this.events.forEach(addEventBytes);

        // Add the end-of-track bytes to the sum of bytes for the track, since
        // they are counted (unlike the start-of-track ones).
        trackLength += endBytes.length;

        // Makes sure that track length will fill up 4 bytes with 0s in case
        // the length is less than that (the usual case).
        var lengthBytes = str2Bytes(trackLength.toString(16), 4);

        return startBytes.concat(lengthBytes, eventBytes, endBytes);
    }
};

window.MidiWriter = MidiWriter;
window.MidiEvent = MidiEvent;
window.MetaEvent = MetaEvent;
window.MidiTrack = MidiTrack;
window.noteTable = noteTable;

})(this);