How to create videos which animate as you draw/write?

An example is of this effect is here: http://www.youtube.com/watch?v=rDu2开发者_JAVA百科A3WzQpo

The standard way to do that type of effect (esp. with text) is to start with a fully masked-out image of your drawing, then animate the mask to reveal the strokes sequentially. Is that what you're asking?

Edit: (re: comments)

Here's a tutorial that goes through a full example (in flash): http://www.gomediazine.com/tutorials/an-angel-grows-wings-animated-mask-in-flash/

The basic idea is that it's easier to animate a simple drawing (like a rectangle, or a spline with a wide stroke-width) than it is to animate a complex one, so you just create the complex one as a still, and then animate the simple one (which is masking the complex one) to simulate drawing. Even though the look of that tutorial is very different from the video, the basic principle is the same.

Here's another simpler example that shows how to mask programmatically (in AS3): http://www.flashandmath.com/intermediate/masking/

You could do something very similar for each line of text (i.e. using a rectangle that covers your text and sweeps left to right to reveal it). More complicated shapes would use the same principle, but would require more complicated masking shapes as well (like in the first tutorial).

Now, of course, you've got the post tagged "Flash", but if you want to actually create strictly video output (as opposed to interactive web output), After Effects is probably a better tool, so here's a link to an AE tutorial for doing something similar:

http://library.creativecow.net/articles/hansen_jaysen/growing/video-tutorial.php