dither4/pack-wav.js

import wavefile from 'wavefile';
let WaveFile = wavefile.WaveFile;

import {
    readFileSync,
    writeFileSync
} from 'fs';

function byte2byte(arr) {
    let lines = [];
    for (let i=0; i < arr.length; i++) {
        lines.push(`.byte ${arr[i]}`);
    }
    return lines.join('\n');
}

class Dither {
    constructor() {
        this.err = 0;
    }

    to4bit(val8) {
        let val = (val8 / 255) - this.err;
        if (val < 0) {
            val = 0;
        }
        if (val > 1) {
            val = 1;
        }
        let val4 = Math.round(val * 15);
        let dithered = (val4 / 15);
        this.err = (dithered - val);
        return val4;
    }
}

function pack(audio) {
    let packed = [];
    let dither = new Dither();
    for (let i = 0; i < audio.length; i += 2) {
        // little-endian 4-bit samples
        let low = dither.to4bit(audio[i]);
        let high = dither.to4bit(audio[i + 1]);
        let byte = low | (high << 4);
        packed.push(byte);
    }
    /*
    // raw push bytes
    for (let i = 0; i < audio.length; i += 2) {
        let val = to4bit(audio[i]);
        let byte = val | 0x10;
        packed.push(byte);
    }
    */
    return packed;
}

function audio2assembly(audio) {
    return `
.segment "AUDIO"

    .export audio_samples
    .export audio_samples_end

audio_samples:
    ${byte2byte(pack(audio))}
audio_samples_end:
    .byte 24

`;
}

function wav2assembly(buffer) {
    let wav = new WaveFile(buffer);
    let samples = wav.getSamples();
    let n = samples.length - (samples.length % 131);
    return audio2assembly(samples.slice(0, n));
}

let infile = process.argv[2];
let outfile = process.argv[3];

let buffer = readFileSync(infile);
let asm = wav2assembly(buffer);
writeFileSync(outfile, asm, 'utf-8');