@fordi-org/wav2msu

wav2msu.js

A library to encode/decode audio data as MSU-1 compatible PCM.

Demo

.wav files should be 16-bit, stereo, 44.1kHz, little-endian. The codec does no data-wrangling. If you need that, there are other JS libs you can wrap around this one.

Based on @jbaiter's wav2msu implementation in C, which was in turn based on Kawa's C# implementation (which is no longer there).

Classes

• WavError extends Error
• MsuError extends Error

These exist so you can differentiate between errors raised when things go wrong.

Functions

wavBufferToRawPcm(wavBuffer:ArrayBuffer):Uint16Array

Reads a WAV buffer, and returns a Uint16Array into its data area.

name	description
wavBuffer	An arraybuffer representing a WAV file.

returns Uint16Array the raw PCM data

rawPcmToMsu(pcm:Uint16Array, { intro?:Uint16Array, loop?:number } = {}):ArrayBuffer

Convert a Uint16Array of samples into an MSU-1 ArrayBuffer.

name	description
pcm	input PCM data, 44.1kHz, stereo, 16 bit
intro	optional intro PCM data, 44.1kHz, stereo, 16 bit
loop	optional loop point specification, if intro not specified

msuToRawPcm(msuBuffer:ArrayBuffer, { packLoop:boolean }):{ loop:Uint16Array, loopPoint:number, intro:Uint16Array }

Convert an MSU-1 ArrayBuffer into a raw PCM Uint16Array

name	description
msuBuffer	input MSU data
packLoop	whether to include the intro and loop into one Uint16Array, or split it between two

rawPcmToWav(pcm:Uint16Array):ArrayBuffer

Convert a Uint16Array of raw samples to a WAV ArrayBuffer

name	description
pcm	input PCM data, 44.1kHz, stereo, 16 bit

Example of use

import { wavBufferToRawPcm, rawPcmToMsu } from '@fordi-org/wav2msu';

const form = document.querySelector('#formMsu1');

// Wrapper to treat a file input as an ArrayBuffer
const fileAsRawPcm = async (fileInput) => {
  if (fileInput.files.length !== 1) {
    throw new Error("No files selected");
  }
  return wavBufferToRawPcm(await fileInput.files[0].arrayBuffer());
};

const pushDownload = (blob, filename) => {
  const url = URL.createObjectURL(blob);
  const link = Object.assign(document.createElement('a'), { href: url, download: targetFilename });
  document.body.appendChild(link);
  link.click();
  document.body.removeChild(link);
}

form.addEventListener('submit', async (e) => {
  // Form handley stuff
  e.preventDefault();
  e.stopPropagation();

  const sourceInput = e.target.querySelector('#source');
  
  const source = await fileAsRawPcm(sourceInput);
  const options = {};
  try {
    options.intro = await fileAsRawPcm(e.target.querySelector('#intro'));
  } catch (e) { // No intro file selected; fail to user-defined loop point
    options.loop = parseInt(e.target.querySelector('#loop').value) ?? 0;
  }
  // Convert to MSU1 ArrayBuffer
  const msu1Buffer = rawPcmToMsu(source, options);

  // Wrap it for download
  const msu1Blob = new Blob([msu1Buffer], { type: "application/octet-stream" });
  const msu1Filename = sourceInput.files[0].name.replace(/\.wav$/, '.pcm');
  pushDownload(msu1Blob, msu1Filename);
  
  return false;
});

See docs/example.js for a more robust example of use.

MSU-1 Format

Near's old Byuu site is gone, so I'm putting this here for posterity. It's relatively simple. Multibyte numbers are little-endian.

name	type	description
magic	string	"MSU1"
loop	uint32	sample number to loop back at
data	uint16*	16-bit, stereo, PCM data

Also, pour one out for Near; they did so much for the emu community.