Transform stream that shifts WebVTT text tracks by the specified offset.
```
npm install vtt-shift
```
Usage
``` js const vttshift = require('vtt-shift') const fs = require('fs') const options = {offsetMs: 1000 // offset in milliseconds
}
fs.createReadStream('some-subtitle-file.vtt')
.pipe(vttshift(options))
.pipe(fs.createWriteStream('some-subtitle-file-shifted-by-1sec.vtt'))
```