Fallback

Hi, happy new year! Could someone guide me to information and possibly products that have the ability to use any type of web video you choose. I am trying to understand how video players (Youtube would be a good example) send video content via Flash and jQuery players that play HTML5 video. I have heard the term Flash fallback, and can’t understand why the fallback would be Flash when I would think it should be falling back on HTML5 when a device other than a computer is accessing it. I was under the impression that with all of the HTML5 video improvement Flash is still the most robust multimedia available when the device can use it. I am aware that the iPhone, iPad, and other popular phones can’t view Flash. Even link to training for how this done and the best practices would be a great help. Thanks