What is XMT

This chapter is dedicated to professionals of 3D graphics industry, solution providers for on-line systems involving 3D content (games, persistent universes, virtual spaces with graphical representation), students and professors in digital sciences. The first section aims at presenting the background of the compression for multimedia signals. The second section presents the latest developments in MPEG-4 with respect to the compression and streaming of 3D graphics objects and scenes. The MPEG-4 tools, categorized into geometry, appearance and animation, are introduced. While MPEG standards specify only the bit-stream syntax and the architecture of the decoder, scheme for encoders’ implementation are presented in this section. In the third section we describe a recently adopted MPEG model for 3D graphics consisting in opening the representation of graphics primitives to any XML-based format and completing it with binarization and compression layers. This shift in the manner of using MPEG-4 for 3D graphics is concretized in Part 25 of MPEG-4 (Preda, Jovanova, Arsov& Prêteux, 2007).