DVD glossary

UDF
Universal Disc Format. Standard developed by the Optical Storage Technology Association. This file system was designed to be able to handle files from all other common file systems (computers), i.e. it can handle Mac resource forks and Windows95 long file names. UDF was also defined to be able to be enhanced for future systems. NSR ECMA 167 and ISO 13346 are predecessors to UDF.

Unidirectional prediction
A form of compression in which the codec uses information only from frames that have already been decompressed.

User Data
All data above the channel layer. This includes Video, Audio, Systems packet overhead, Subpictures, Navigation data, DSI packets, and File Management data. DVD reference data rate is specified as 11.08 mbit/sec.

User interface
A lowest common denominator of functions providing interactive selection of disc programming content. Includes: Ten keys and cursor keys, menu graphics and highlight areas, menu still picture with subpicture, and MPEG graphics.