keyframes make it possible (Score 1)

Mpeg like most other video compression schemes uses key frames. Every so many frames it does 1 complete frame that doesn't rely on the previous frames to generate an image. Start the tape and it will give you nothing for a couple of seconds until it hits a key frame then the video starts. Digital cable and DSS television work this way. Ever wonder why it takes more time to change channels than with analog? Thats why.