Media Foundation IMFSourceReaderCallback::OnReadSample Callback timestamp parameter

Regarding the MFCaptureD3D sample from the media foundation examples, which can be found here

http://msdn.microsoft.com/en-us/library/windows/desktop/ms702261%28v=vs.85%29.aspx

The Timestamp in the OnReadSample is has the same value as the attribute MFSampleExtension_DeviceTimestamp from the sample, but how can I interpret this value ?

I need to translate this timestamp to the system time or convert it to a DateTime object.