srt-to-vtt/mod.ts

// SPDX-License-Identifier: MIT

/**
 * @param {string} data SRT text to be converted
 * @returns {string} VTT text
 */
export default function srt2webvtt(data: string): string {
  // remove dos newlines
  let srt = data.replace(/\r+/g, "");
  // trim white space start and end
  srt = srt.replace(/^\s+|\s+$/g, "");

  // get cues
  const cuelist = srt.split("\n\n");
  let result = "";

  if (cuelist.length > 0) {
    result += "WEBVTT\n\n";
    for (let i = 0; i < cuelist.length; i = i + 1) {
      result += convertSrtCue(cuelist[i]);
    }
  }

  return result;
}

/**
 * @param {string} caption SRT section for parsing
 * @returns {string} translated VTT section
 */
function convertSrtCue(caption: string): string {
  // remove all html tags for security reasons
  //srt = srt.replace(/<[a-zA-Z\/][^>]*>/g, '');

  let cue = "";
  const s = caption.split(/\n/);

  // concatenate muilt-line string separated in array into one
  while (s.length > 3) {
    for (let i = 3; i < s.length; i++) {
      s[2] += "\n" + s[i];
    }
    s.splice(3, s.length - 3);
  }

  let line = 0;

  // detect identifier
  if (!s[0].match(/\d+:\d+:\d+/) && s[1].match(/\d+:\d+:\d+/)) {
    cue += s[0].match(/\w+/) + "\n";
    line += 1;
  }

  // get time strings
  if (s[line].match(/\d+:\d+:\d+/)) {
    // convert time string
    const m = s[1].match(
      /(\d+):(\d+):(\d+)(?:,(\d+))?\s*--?>\s*(\d+):(\d+):(\d+)(?:,(\d+))?/,
    );
    if (m) {
      cue += m[1] +
        ":" +
        m[2] +
        ":" +
        m[3] +
        "." +
        m[4] +
        " --> " +
        m[5] +
        ":" +
        m[6] +
        ":" +
        m[7] +
        "." +
        m[8] +
        "\n";
      line += 1;
    } else {
      // Unrecognized timestring
      return "";
    }
  } else {
    // file format error or comment lines
    return "";
  }

  // get cue text
  if (s[line]) {
    cue += s[line] + "\n\n";
  }

  return cue;
}