Based on @mafintosh's work on srt-to-vtt.
Transform stream that converts ass files to vtt files. vtt files are used to provide subtitles in html5 video
npm install ass-to-vtt
var ass2vtt = require('ass-to-vtt')
var fs = require('fs')
fs.createReadStream('some-subtitle-file.ass')
.pipe(ass2vtt())
.pipe(fs.createWriteStream('some-html5-video-subtitle.vtt'))
There is also a command line tool available
npm install -g ass-to-vtt
ass-to-vtt --help
MIT