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import { messageTypes } from "./midi_message.js";
import { writeVariableLengthQuantity } from "../utils/byte_functions/variable_length_quantity.js";
import { writeBytesAsUintBigEndian } from "../utils/byte_functions/big_endian.js";
/**
* Exports the midi as a standard MIDI file
* @this {BasicMIDI}
*/
export function writeMIDI()
{
const midi = this;
if (!midi.tracks)
{
throw new Error("MIDI has no tracks!");
}
/**
* @type {Uint8Array[]}
*/
const binaryTrackData = [];
for (const track of midi.tracks)
{
const binaryTrack = [];
let currentTick = 0;
let runningByte = undefined;
for (const event of track)
{
// Ticks stored in MIDI are absolute, but SMF wants relative. Convert them here.
const deltaTicks = event.ticks - currentTick;
/**
* @type {number[]}
*/
let messageData;
// determine the message
if (event.messageStatusByte <= messageTypes.sequenceSpecific)
{
// this is a meta-message
// syntax is FF<type><length><data>
messageData = [0xff, event.messageStatusByte, ...writeVariableLengthQuantity(event.messageData.length), ...event.messageData];
}
else if (event.messageStatusByte === messageTypes.systemExclusive)
{
// this is a system exclusive message
// syntax is F0<length><data>
messageData = [0xf0, ...writeVariableLengthQuantity(event.messageData.length), ...event.messageData];
}
else
{
// this is a midi message
messageData = [];
if (runningByte !== event.messageStatusByte)
{
// Running byte was not the byte we want. Add the byte here.
runningByte = event.messageStatusByte;
// add the status byte to the midi
messageData.push(event.messageStatusByte);
}
// add the data
messageData.push(...event.messageData);
}
// write VLQ
binaryTrack.push(...writeVariableLengthQuantity(deltaTicks));
// write the message
binaryTrack.push(...messageData);
currentTick += deltaTicks;
}
binaryTrackData.push(new Uint8Array(binaryTrack));
}
/**
* @param text {string}
* @param arr {number[]}
*/
function writeText(text, arr)
{
for (let i = 0; i < text.length; i++)
{
arr.push(text.charCodeAt(i));
}
}
// write the file
const binaryData = [];
// write header
writeText("MThd", binaryData); // MThd
binaryData.push(...writeBytesAsUintBigEndian(6, 4)); // length
binaryData.push(0, midi.format); // format
binaryData.push(...writeBytesAsUintBigEndian(midi.tracksAmount, 2)); // num tracks
binaryData.push(...writeBytesAsUintBigEndian(midi.timeDivision, 2)); // time division
// write tracks
for (const track of binaryTrackData)
{
// write track header
writeText("MTrk", binaryData); // MTrk
binaryData.push(...writeBytesAsUintBigEndian(track.length, 4)); // length
binaryData.push(...track); // write data
}
return new Uint8Array(binaryData);
} |