I use adobe premiere and I records with dxtory and then I change codecs my cpu uses different amounts of CPU for the render, is that normal. Here is what I mean: http://gyazo.com/ba9ac35c8eac0e1cfb0712a2972cb46b
I use lagarith and h.264
This range of fluctuation is quite normal when rendering, especially when using different codecs.Don't worry about it. Even if it was going from 60%-100%, there really shouldn't be a problem. And also, different codecs stress the CPU in varying amounts.