ass_to_vtt.js

'use strict';

var fs 			= require('fs'),
	readline 	= require('readline');

var ass_to_vtt = (file_in, file_out, cb)=>{
	var reg = /Dialogue: [0-9],([0-9]:([0-9]{2}):[0-9]{2}.[0-9]{2}),([0-9]:([0-9]{2}):[0-9]{2}.[0-9]{2}).*,,(.*)/g;
	fs.writeFileSync(file_out, 'WEBVTT\n\n');
	readline.createInterface({
  		input: fs.createReadStream(file_in)
  	}).on('line', (line)=>{
  		var explode = line.split(reg);
  		if(explode.length == 7){
	  		var	start = '0' + explode[1],
	  		end = '0' + explode[3],
	  		txt = explode[5],
	  		vtt = (start + ' --> ' + end + '\n' + txt + '\n\n');
			fs.appendFileSync(file_out, vtt);
		}
	}).on('close', ()=>{
		cb(true);
	});
};

ass_to_vtt('English.ass', 'English.vtt', ()=>{
	console.log('done');
});

Node js function

translate a ass subtitles to vtt subs. nice for html5.