How to get 100% CPU usage on video conversion?

You will never get full 100% CPU usage on a video conversion because if all the CPU's resources were being used to do that your computer itself could not do the other REQUIRED functions that it would need to operate. The point to having a dual or quad processor is so that there is an equal balance of use from all the processors so instead of 1 giving you 60 -90% CPU usage, it will combine 25 - 30% from each processor. You would also need more than 8GB memory to get even near that usage because your processors will not use the entire 8GB of memory. It will use closer to 3 or 4GB, depending on how much memory your video memory will allow you to use.