When you use Windows 8 Camera app to capture a high definition resolution (i.e. 1080p) video, you may notice that during playback of the video it appears to be faster than real time. This behavior is more noticeable on PCs with lower end CPUs. To work around this issue, try capturing the video in the Camera app using a lower video resolution (i.e. 720p, 540p or 480p).
Microsoft has released the Windows Assessment and Deployment Kit (ADK) to help measure the performances of the underlying hardware and suggest or provide improvements where available. For more information about this toolkit, click on the following link: http://msdn.microsoft.com/en-us/library/windows/hardware/hh825508.aspx