I've been learning more about how Windows Media Center Presentation Layer Applications are run on the XBox 360 Media Center Extender. For a while now I've been stating these apps render at 30 Frames Per Second (FPS). As the Hertz commercial says, well...'not exactly'.

But unlike the Hertz commercial, this 'not exactly' is a good thing.

As Paul Harvey would say, here is the rest of the story...

For a Windows Media Center Presentation Layer Application, the Windows Media Center Rendering Engine running on the XBox 360 combines the video signal (deinterlacing when necessary) with the user interface and renders both to match the current frame rate of the display. On the XBox 360 in the United States that means you get a refresh rate of 60 Hz or Frames Per Second. (It's worth noting the XBox 360 native refresh rate can be different depending on the geography.) Generally speaking, the higher the refresh rate, the smoother the experience appears to the user and less noticeable flicker.

By contrast, the Hosted HTML or Hosted WinFX XBAP Application user interfaces are rendered on the Media Center PC with 3-5 screenshots taken per second (on average) which are sent over the network via a Remote Desktop-like pipe. Even though the XBox 360 display output is much higher these applications will appear to operate at a much lower framerate due to the rate at which screenshots are sent.

So, why have I been saying '30 FPS' for the last couple of months? It's what I knew from my work with the Windows Media Encoder (NTSC television is shot at 30 FPS and output to your TV at 60 Hz, film is shot at 24 FPS and typically projected at 72 FPS using the shutter to avoid flicker) and was the best way I could describe at the time how the three types of applications will appear to the end user. My apologies to our readers for not getting the facts 100% straight before posting / answering questions. In this case I hope you will say 'no harm, no foul'.

If you want to learn more about refresh rates, head on over to Wikipedia at http://en.wikipedia.org/wiki/Frame_rate.

Francis Hogle (Development Manager for the Windows Media Center team) is preparing a four part series which explains how this stuff works in greater detail -- look for it here soon.

Charlie