node_modules/@k-l-lambda/music-widgets/source/inc/MIDI/midifileEx.js

/*
class to encode the .mid file format
(depends on streamEx.js)
*/

const OStream = require("./streamEx.js");



module.exports = function OMidiFile ({ header, tracks }) {
	function writeChunk (stream, id, data) {
		console.assert(id.length === 4, "chunk id must be 4 byte");

		stream.write(id);
		stream.writeInt32(data.length);
		stream.write(data);
	}

	function writeEvent (stream, event) {
		if (event.subtype === "unknown")
			return;

		stream.writeVarInt(event.deltaTime);

		switch (event.type) {
		case "meta":
			stream.writeInt8(0xff);

			switch (event.subtype) {
			case "sequenceNumber":
				stream.writeInt8(0x00);
				stream.writeVarInt(2);

				stream.writeInt16(event.number);

				break;
			case "text":
				stream.writeInt8(0x01);
				stream.writeVarInt(event.text.length);

				stream.write(event.text);

				break;
			case "copyrightNotice":
				stream.writeInt8(0x02);
				stream.writeVarInt(event.text.length);

				stream.write(event.text);

				break;
			case "trackName":
				stream.writeInt8(0x03);
				stream.writeVarInt(event.text.length);

				stream.write(event.text);

				break;
			case "instrumentName":
				stream.writeInt8(0x04);
				stream.writeVarInt(event.text.length);

				stream.write(event.text);

				break;
			case "lyrics":
				stream.writeInt8(0x05);
				stream.writeVarInt(event.text.length);

				stream.write(event.text);

				break;
			case "marker":
				stream.writeInt8(0x06);
				stream.writeVarInt(event.text.length);

				stream.write(event.text);

				break;
			case "cuePoint":
				stream.writeInt8(0x07);
				stream.writeVarInt(event.text.length);

				stream.write(event.text);

				break;
			case "midiChannelPrefix":
				stream.writeInt8(0x20);
				stream.writeVarInt(1);

				stream.writeInt8(event.channel);

				break;
			case "endOfTrack":
				stream.writeInt8(0x2f);
				stream.writeVarInt(0);

				break;
			case "setTempo":
				stream.writeInt8(0x51);
				stream.writeVarInt(3);

				stream.writeInt8((event.microsecondsPerBeat >> 16) & 0xff);
				stream.writeInt8((event.microsecondsPerBeat >> 8) & 0xff);
				stream.writeInt8(event.microsecondsPerBeat & 0xff);

				break;
			case "smpteOffset":
				stream.writeInt8(0x54);
				stream.writeVarInt(5);

				var frameByte = { 24: 0x00, 25: 0x20, 29: 0x40, 30: 0x60 }[event.frameRate];
				stream.writeInt8(event.hour | frameByte);
				stream.writeInt8(event.min);
				stream.writeInt8(event.sec);
				stream.writeInt8(event.frame);
				stream.writeInt8(event.subframe);

				break;
			case "timeSignature":
				stream.writeInt8(0x58);
				stream.writeVarInt(4);

				stream.writeInt8(event.numerator);
				stream.writeInt8(Math.log2(event.denominator));
				stream.writeInt8(event.metronome);
				stream.writeInt8(event.thirtyseconds);

				break;
			case "keySignature":
				stream.writeInt8(0x59);
				stream.writeVarInt(2);

				stream.writeInt8(event.key);
				stream.writeInt8(event.scale);

				break;
			case "sequencerSpecific":
				stream.writeInt8(0x7f);
				stream.writeVarInt(event.data.length);

				stream.write(event.data);

				break;
			default:
				throw new Error("unhandled event subtype:" + event.subtype);
			}

			break;
		case "sysEx":
			stream.writeInt8(0xf0);
			stream.writeVarInt(event.data.length);
			stream.write(event.data);

			break;
		case "dividedSysEx":
			stream.writeInt8(0xf7);
			stream.writeVarInt(event.data.length);
			stream.write(event.data);

			break;
		case "channel":
			switch (event.subtype) {
			case "noteOn":
				stream.writeInt8(0x90 | event.channel);
				stream.writeInt8(event.noteNumber);
				stream.writeInt8(event.velocity);

				break;
			case "noteOff":
				stream.writeInt8(0x80 | event.channel);
				stream.writeInt8(event.noteNumber);
				stream.writeInt8(event.velocity ? event.velocity : 0);

				break;
			case "noteAftertouch":
				stream.writeInt8(0xa0 | event.channel);
				stream.writeInt8(event.noteNumber);
				stream.writeInt8(event.amount);

				break;
			case "controller":
				stream.writeInt8(0xb0 | event.channel);
				stream.writeInt8(event.controllerType);
				stream.writeInt8(event.value);

				break;
			case "programChange":
				stream.writeInt8(0xc0 | event.channel);
				stream.writeInt8(event.programNumber);

				break;
			case "channelAftertouch":
				stream.writeInt8(0xd0 | event.channel);
				stream.writeInt8(event.amount);

				break;
			case "pitchBend":
				stream.writeInt8(0xe0 | event.channel);
				stream.writeInt8(event.value & 0xff);
				stream.writeInt8((event.value >> 7) & 0xff);

				break;
			default:
				throw new Error("unhandled event subtype:" + event.subtype);
			}

			break;
		default:
			throw new Error("unhandled event type:" + event.type);
		}
	}

	const stream = new OStream();

	const headerChunk = new OStream();
	headerChunk.writeInt16(header.formatType);
	headerChunk.writeInt16(tracks.length);
	headerChunk.writeInt16(header.ticksPerBeat);

	writeChunk(stream, "MThd", headerChunk.getBuffer());

	for (let i = 0; i < tracks.length; ++i) {
		const trackChunk = new OStream();

		for (let ei = 0; ei < tracks[i].length; ++ei)
			writeEvent(trackChunk, tracks[i][ei]);

		writeChunk(stream, "MTrk", trackChunk.getBuffer());
	}

	return stream.getArrayBuffer();
};