The Games Factory .gam 0C_Music.mus music file to midis converter

tgf-midi-extractor.mjs

// The Games Factory 0C_Music.mus -> midi files
// See the following tool for actually extracting the 0C_Music.mus file from a .gam file
// https://kippykip.com/threads/cextract-the-games-factory-multimedia-fusion-game-extractor-unprotector.498/
//
import fs from 'fs'

const input = './0C_Music.mus'

const buffer = fs.readFileSync(input)

let chars = []

for(let i = 0; i < buffer.length; i++) {
	const value = buffer[i]
	const char = String.fromCharCode(value)
	chars.push(char)
}

const midiStartIndexes = findSections(chars, ['M', 'T', 'h', 'd'])

// Array to store the result buffers with the MIDI files.
let midiBuffers = []

for(let i = 0; i < midiStartIndexes.length; i++) {
	let startIndex = midiStartIndexes[i]
	let endIndex   = midiStartIndexes[i + 1]
	
	const midiBuffer = buffer.subarray(startIndex, endIndex)
	midiBuffers.push(midiBuffer)
}

for(let i = 0; i < midiBuffers.length; i++) {
	const midiBuffer = midiBuffers[i]
	fs.writeFileSync(`./midi-${i}.mid`, midiBuffer, {encoding: null})
}
console.log('done writing')
// console.log(midiBuffers)


// Find all starting indexes of the findArray within the fromArray
function findSections(fromArray, findArray) {
	// Basic validation: if findArray is empty or larger than fromArray, it can't be found
	if (findArray.length === 0 || findArray.length > fromArray.length) {
		return undefined;
	}

	const results = [];

	// Loop through the array, but stop where the remaining length 
	// is shorter than the array we are looking for.
	for (let i = 0; i <= fromArray.length - findArray.length; i++) {
		let match = true;

		// Check if the sequence starting at i matches findArray
		for (let j = 0; j < findArray.length; j++) {
			if (fromArray[i + j] !== findArray[j]) {
				match = false;
				break;
			}
		}

		if (match) {
			results.push(i);
		}
	}

	// Return the results array if it contains items, otherwise return undefined
	return results.length > 0 ? results : undefined;
}