Hello Skorpionim, my name is Volodymyr and I am flash-developer. I have great experience in working with flash and ActionScript 3.0. I am familiar with design patterns and I have experience in building a software architecture. I always do it flexible and scalable. So there is no problem with, for example, Undo/Redo functionality or with changing themes. I have published applications on AIR platform, so can be sure that application will work on Windows and Mac. I must confess that I have never worked with creating video using AS3, but there are libraries that will help to create video. Yes I understand that the key features of your application is creating and exporting video, but there are many other features that need correctly built software architecture that I can develop.
Thanks.