Generate subtitles SRT file from raw text file

txt-to-srt.js

const { readFileSync, writeFileSync } = require("fs");

function getFormattedTime(timeMilliseconds) {
  return new Date(timeMilliseconds).toISOString().substring(11, 23);
}

const REPLACEMENT_PROBABILITY = 0.01;
const REPLACEMENT_CHARACTERS = "✴⦧⦖";
function getRandomlyReplacedText(text) {
  if (REPLACEMENT_PROBABILITY === 0) {
    return text;
  }
  const replacementCharacters = REPLACEMENT_CHARACTERS.split("").sort(
    () => 0.5 - Math.random()
  );
  return text
    .split("")
    .map((originalCharacter) => {
      return Math.random() > REPLACEMENT_PROBABILITY
        ? originalCharacter
        : replacementCharacters.length
        ? replacementCharacters.shift()
        : originalCharacter;
    })
    .join("");
}

function main() {
  const lines = readFileSync("./input.txt").toString().split("\n");

  const subtitlesWithMetadata = [];
  for (let index = 0; index < lines.length; index++) {
    const line = lines[index];
    const endTimePrevious = index
      ? subtitlesWithMetadata[index - 1].endTime
      : 0;
    const isPreviousLineEmpty = index && !lines[index - 1];
    const startTime = endTimePrevious + (isPreviousLineEmpty ? 1500 : 0);

    subtitlesWithMetadata.push({
      startTime,
      endTime: startTime + (line ? 3000 : 0),
      content: line,
    });
  }

  const srtSubtitles = subtitlesWithMetadata
    .filter(({ content }) => content)
    .map(
      ({ startTime, endTime, content }, index) => `${index + 1}
${getFormattedTime(startTime)} --> ${getFormattedTime(endTime)}
${getRandomlyReplacedText(content)}`
    )
    .join("\n\n");

  writeFileSync(
    `./output-${new Date().toISOString().replace(/:/g, "-")}.srt`,
    srtSubtitles,
    "utf-8"
  );
}

main();