They used AutoGK as stated on that page. You'll get that performance increase because Windows dynamically schedules threads for the least busy CPU.. you'll see what kind of CPU usage you get but normally without any special encoder optimization (so they'd have to be in the XviD or DivX codec), you won't get 99% usage on both cores. The experience with the x264 codec, which has undergone some SMP optimizations, shows that CPU usage of both cores went up considerably with the optimized version (but you'll never reach 99% on both). It is not always easy to make SMP optimizations because for ideal cpu use you need to rip each frame to be encoded apart, encode parts on different cores, and put it back together. In MPEG-4 AVC, since frames can be put into different slices, this is probably a more straightforward task than for codec specs that do not forsee such mechanisms.