In .mov for QuickTime 7 (two videos)
In .rm for Real Player (one video)
In .mp4 for most computers (two videos)
Two videos are proposed here, the first one relates what I do with my computer, and the second shows how I write.

On the left, choose the best format for your computer. The best quality is QuickTime 7, you can download (free) QuickTime 7 from the web site :