In Windows 8, users are allowed to capture a short video using webcam and use the video as the user account picture. I want to know what format is that video in, so I can override it with my custom video. I do not have a webcam so I cannot test it myself. I have tried .avi and .wmv but none of them works.
You can follow this guide
The guide contain additional tricks like using a bitmap and video as User Tile at the same time
Note: I tried using the browse function on my own PC, but it cannot open any video formats I know of. MP4, MPG, M4V, WMV or AVI. WMV would be the most logical choice for Windows, since it's named Windows Media Video