How much CPU is used depends on many different factors. For example, if your profile is using hardware encoding with a supported hardware encoder (you logs will tell you that), the core conversion may be handled by the GPU. However if your profile is asking for tasks like say decoming or deinterlacing which you GPU man not support, then it falls back to the CPU for that. Then there are other tasks, like metadata processing, remuxing, commercial removal etc which are purely CPU intensive tasks. GPU’s for the most take off the bulk of encoding processing from the CPU but there may still be things the CPU needs to do which the GPU does not depending on the profile and hardware.
For the rest of the CPU work you can still limit how much CPU MCEBuddy uses using the tools as explained in this post so it doesn’t impact the responsiveness or resources available for other tasks in your computer:
I’m having the same problem all of a sudden. I have changed nothing except I ran and MKV H.265 conversion earlier and my GPU didn’t support H.265 so it ran an all software encode with handbrake using all my available CPU pushing utilization to 100%.
I went out after dinner and bought an new video card. Now HEVC conversions are super fast but CPU utilization are still 100% so I and running one now using MKV Normal Quality as I always have and now my CPU utilization is still 100% where it used to be about 65% running the same encoding profile.
I solved the problem, I went into the config folder and edited the profiles file to change the order of encoders and put ffmpeg first…now my CPU utilization is down to 50% with the same encoding times.