Taken from Wikipedia
Tarkin is an experimental lossy video codec formerly under development by the Xiph.org Foundation. Tarkin has been put on hold, with Theora becoming the main focus for video encoding.
Tarkin is based on 3-D wavelet compression. A block of video has three dimensions, two spatial and one temporal, and is encoded as a unit with a 3-D discrete wavelet transform. This is in stark contrast to the more traditional method used in Theora and most other video codecs of doing a 2-D discrete cosine transform on single frames of video and doing inter-frame differences and perhaps motion compensation in a separate step.
Tarkin was named after Grand Moff Tarkin from the movie Star Wars.