Xvid (formerly XviD) is an open source MPEG-4
video codec, implementing MPEG-4 Simple Profile,
Advanced Simple Profile, and Advanced Video Coding
standards. It is written in C with assembler
optimizations for quality and speed (including
MMX, SSE, and 3Dnow! code for i386 and AltiVec for
PowerPC), and is especially optimized towards
offline, multi-pass compression for storage and
archival purposes.