Supercession is by definition the act of a media class to include, further classify, or incorporate into a more comprehensible form of media before the inclusion took place. A better definition by Gitelman and Pingree states that supercerssion is "the notion that each new medium "vanquishes or subsumes its predecessors."
Beta > VHS > LaserDisc > DVD > HD-DVD/BLU-RAY > UHDV (Soon) ▼
> VHS > LaserDisc > DVD > HD-DVD/BLU-RAY > UHDV (Soon)
In this regard, each iteration of what we refer to as the medium we watch our movies on has taken from past generations of mediums, improved on the ideas and technological usage, and produced a format that 1-upped the previous generation in terms of quality, storage capacity, or cost.