audacity-labels-to-vtt.js

#!/usr/bin/env node
/**
 * Script for converting Audacity labels to WebVTT.
 *
 * This reads audacity labels from a .txt file passed as an argument to the script,
 * and outputs the WebVTT to standard out.
 *
 * Usage:
 * ./audacity-labels-to-vtt.js path/to/audacity/labels/file.txt > path/to/file.vtt
 */
import { readFileSync } from 'node:fs';
import process from 'node:process';

if (process.argv.length < 3) {
    console.log(`Usage: ./audacity-labels-to-vtt.js <path/to/audacity/labels.txt>`)
    process.exit(1);
}

const filename = process.argv[2];

const audacityLabels = readFileSync(filename, 'utf-8', err => { if (err) throw err });

/**
 * Adapted from:
 * https://github.com/magcius/audaciter/blob/699d467925fe0a194fe62fa1e0f73bea1cfd6fba/func.js
 */
function audacityLabelsToSrt(audacityLabels) {
    function parseLabelTime(timestamp) {
        // This is a horrible idea.
        var parsed = timestamp.split('.', 2);
        var secs = parsed[0], msecs = parsed[1];
        return parseInt(secs, 10) * 1000 + parseInt(msecs.slice(0, 3), 10);
    }

    function parseLabels(lines) {
        var labels = [];

        lines.forEach(function(line) {
            line = line.trim();

            if (!line)
                return;

            if (line.startsWith('#'))
                return;

            var parsed = line.match(/(.*?)\s+(.*?)\s+(.*)/);
            var start = parseLabelTime(parsed[1]);
            var stop = parseLabelTime(parsed[2]);
            var message = parsed[3];
            labels.push({ start: start, stop: stop, message: message });
        });

        return labels;
    }

    function srtTimecode(msecs) {
        var ms = Math.floor(msecs % 1000);
        var value = msecs / 1000;

        var s = Math.floor(value % 60);
        value = value / 60;

        var m = Math.floor(value % 60);
        var h = Math.floor(value / 60);

        function pad(n, z) {
            n = '' + n;
            while (n.length < z)
                n = '0' + n;
            return n;
        }

        return (pad(h, 2) + ':' + pad(m, 2) + ':' + pad(s, 2) + ',' + pad(ms, 3));
    }

    function formatSrtChunk(label, i) {
        var lines = [];

        lines.push('');
        lines.push(i + 1);
        lines.push(srtTimecode(label.start) + ' --> ' + srtTimecode(label.stop));
        lines.push(label.message);

        return lines.join('\n');
    }

    var lines = audacityLabels.split('\n');
    var srt = parseLabels(lines).map(formatSrtChunk).join('\n');
    return srt;
}

/**
 * Adapted from:
 * https://github.com/imshaikot/srt-webvtt/blob/467121344c358cec78876d7fca2496d74d55115d/index.ts#L42-L48
 */
function srtToVtt(srt) {
  return 'WEBVTT\n' + srt
    .replace(/\{\\([ibu])\}/g, '</$1>')
    .replace(/\{\\([ibu])1\}/g, '<$1>')
    .replace(/\{([ibu])\}/g, '<$1>')
    .replace(/\{\/([ibu])\}/g, '</$1>')
    .replace(/(\d\d:\d\d:\d\d),(\d\d\d)/g, '$1.$2')
    .concat('\n');
}

console.log(srtToVtt(audacityLabelsToSrt(audacityLabels)));