You may also want to incorporate advertising into your video delivery system, via an ad network.
In a nutshell
You'll need to work with your ad partners to migrate to HTML. Generally speaking, ad formats such as VAST and VPAID 2.0 are supported in HTML5. Many commercial video players support VAST/VPAID, such as Cedato, JWPlayer, and Video.js.
You need to ensure that your chosen player integrates effectively with your ad partner (FreeWheel, DoubleClick, etc., can answer questions and provide help with choosing a solution that works for you).