Alex has looked into more of the technical details behind how NBC is streaming the Olympics, and has made an interesting discovery. Apparently the stream formats are different for live streams vs. pre-recorded streams. This means that you can make digital recordings of live events, and record from the screen for “rewind” or cached events. Below is his technical summary.
The Silverlight NBC Olympics server uses Windows Media Player for live streams and VP7 for prerecorded videos. VP7 is the format used by web sites like abc.com or fox.com and can provide very high quality (lossless) video compression including HD. The problem with this format is that it cannot be reliably streamed for longer periods of time like the live broadcasts. The math used to compress the video and the audio does not allow recovery when packets are lost which results in out of sync audio. Currently Windows Media Player is the only format that can do this. The live stream Olympics can be recorded with WM Recorder or Replay Media Catcher but the prerecorded clips can only be recorded with WM Capture.