Is it actually going to be embedded into the HTML of a web site? If so, we can show you how -- but you'll need to know the dimensions (in pixels) of the window they're going to place your video in.
If you're going to post to a social media site, like Facebook, YouTube or Vimeo, it's much easier. You simply output a web-optimized MP4 and the site will convert it into a format that works on their site.
So it all depends on if this is an actually-designed web page or just a link to a social media site.