native-lyrics-tools/src/ass.js

A JavaScript library for parsing and generating various lyric formats.

function writeTimestamp(time) {
  const ms = time % 1000;
  const sec = Math.floor(time / 1000);
  const min = Math.floor(sec / 60);
  const hour = Math.floor(min / 60);

  return `${hour}:${String(min % 60).padStart(2, '0')}:${String(sec % 60).padStart(2, '0')}.${String(Math.floor(ms / 10)).padStart(2, '0')}`;
}

export function stringifyAss(lines) {
  let result = `[Script Info]
[Events]
Formats: Marked, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
`;

  for (const line of lines) {
    if (!line.words?.length) continue;

    const startTime = Math.min(...line.words.map(w => w.start_time));
    const endTime = Math.max(...line.words.map(w => w.end_time));

    const name = `${line.is_duet ? "v2" : "v1"}${line.is_bg ? "-bg" : ""}`;

    const kText = line.words.map(word => {
      const duration = Math.floor((word.end_time - word.start_time) / 10);
      return `{\\k${duration}}${word.word}`;
    }).join('');

    result += `Dialogue: 0,${writeTimestamp(startTime)}, ${writeTimestamp(endTime)}, Default, ${name},0,0,0,,${kText}\n`;

    if (line.translated_lyric) {
      result += `Dialogue: 0,${writeTimestamp(startTime)}, ${writeTimestamp(endTime)}, Default, ${name}-trans,0,0,0,,${line.translated_lyric}\n`;
    }

    if (line.roman_lyric) {
      result += `Dialogue: 0,${writeTimestamp(startTime)}, ${writeTimestamp(endTime)}, Default, ${name}-roman,0,0,0,,${line.roman_lyric}\n`;
    }
  }

  return result;
}