John Udell has more comments and comparisons with various media formats.
In terms of viewing convenience, the Silverlight example exhibits a nice property that I wasn’t expecting. When you resize the window containing the player, the player scales to fit. I’m pretty sure the embeddable Quicktime and Windows Media players can’t do that. Flash-based media players are more customizable, and can respond to container resize events, but I don’t think I’ve ever seen the technique applied to a screencast. It’s a nice idea. A screencast at 1:1 resolution is guaranteed to be legible, but will also consume a lot of screen real estate. So it’s tempting to shrink its width and height in production. But by how much? Any fixed resolution will work well for some people and not others. Resizable screencasts would be great for accessibility.