Is there a quick way to convert a Flash site to HTML5? That's the question we're being asked more often as hardware manufacturers drop their support for Flash and Adobe's once major software starts getting marginalized. While Adobe still has plans for future Flash development, it is clearly no longer the medium of choice for current and future web projects.
The answer to the conversion question is - it depends. There are technologies for converting basic SWF animations into HTML5 and CSS. The resulting animation's code will still need to be cleaned by hand, but it does not need to be recreated from scratch. This will only work with simple, timeline-driven animations, such as banners, as all project assets are exported as individual elements and timeline is converted into script.
If your Flash site is driven by a content management system these conversion technologies will not work, as all the Flash interactivity is programmed in scripts, not in timeline. In this case, Flash to HTML5 conversion needs to be a rebuild of the entire front end. The good news is that CSS and JavaScript animations have come such a long way that they can closely approximate the Flash aesthetic, which (apart from custom fonts) was the main reason designers used to choose Flash for their projects. And of course, your CMS remains intact and can be readily integrated into the new HTML5 front end. The overall silver lining is that by converting to HTML5 you can incorporate new technologies such as responsive build, which address a wide range of devices, some not even supporting Flash, and guarantee your site's accessibility for the next decade as HTML5 becomes the dominant standard of building for web.