To get an idea of how to use my WebVfx framework to do what you want have a look at the “User Supplied” section of my webpage at http://www.elusien.co.uk/shotcut/
See the forum thread HTML Filters: Titles, Scrolling Credits, Stopwatches, Gauges etc as well.
Also, check out the video there showing basic examples of what it can do. If you need any help just let me know, - Neil.