What do you need to get started?
I would need all the related Flash or Flex files. Also the assets, in case they are called externally.
What HTML5 API do you use?
I use Create JS, Open FL / Haxe and Zim JS for porting flash to html 5.0
If your SWF is small and simple you may try a software to convert it to html5.0. This is a quick and easy solution for simple SWF applications. Please find more details on my blog here: Quick and Easy Flash to Html5.0 conversion.
Canvas has given HTML5.0 immense capabilities. In fact it can offer functionalities that Flash was known for to offer previously. Flash ruled internet because of it's graphics and animation capabilities which no other web based script could offer at that time. No matter it's for tweening or sprite based animations. And all that came with easy to learn script called AS3.0 ( Actionscript ).
Most things with Flash can now be achieved by HTML5.0’s canvas too. Though there are still some issues HTML5.0 struggles with, as compared to Flash, for example speed, processing power, and audio support but the biggest advantage of HTML5.0 over Flash is it’ ability to work on smartphones and tablets. And it's much expected that all the current drawbacks of HTML5.0 canvas will soon be overcome with new updates in the browsers and the API itself.
Now let's say you have got an old Flash application, which you or your team took a lot of time to get developed. But now since swf plugin will be obsolete after 2020, it clearly means that the time and money spent to develop the app and the idea proved to be a complete waste.
But here is the good news. Since HTML5.0 canvas can offer many functionalities similar to Flash, the flash application can be ported directly to HTML5.0, with minimum differences.
Open FL API boasts to provide a set of API very similar to Actionscipt, while Create JS is officially supported by Adobe in Animate CC IDE, ZimJS is built over Create JS, and is very powerful. In all the three cases the graphics and animations can be easily reused. As all three of them can also connect with Adobe Animate CC IDE which is the new name and advanced version of Flash IDE.
Since it may not be practicable to port each and every component and animation, you will first need to provide the related Flash files for a review. After reviewing and going through all the aspects, I would be able to tell you the feasibility or the extent of porting the Flash file to HTML5.0. If you still have confusions regarding the process, kindly drop me a line so that I may help you understand it.
Thank you. :)