Welcome to VTTCaptions.com.
The webVTT format is the HTML5 standard for video subtitles - otherwise known as 'closed captions', and since I am just beginning to use captions on my videos for various reasons - SEO being amongst them - I wanted to find a simple way of turning a script or transcript into a webVTT file: I wanted to do the following things:
The bad news is, I couldn't find what I wanted.
The good news is, you can. In fact you just have. Oh yes - and it's free.
The Caption Generator on this site does everything on my list, and (I think) supports everything in the webVTT standard.
A word of caution there, though: at the time of writing (May 2013) most embedded video players (jwPlayer, FlowPlayer, YouTube etc) only support a subset of the webVTT standard, some don't support webVTT (yet), and some (like Vimeo) don't support closed captions at all, and browser support is variable (more info here)
The Caption Generator is a work in progress, so please let me know if there's anything buggy or if you want a feature added.
And the instructions on using the Caption Generator are rudimentary at best, and largely missing - I'm working on it...!
All the best,