Q: my mac book gets how on recording with Quick time

Does the Mac shutdown unexpectedly when recording? If not it is probably normal. Computers will use fans to cool when they are busy running complex tasks. You may want to get a a stand or riser that can improve airflow if you must record the screen a lot. Displaying & recording thousands of pixels can strain laptops, you could see if lower resolution settings make any difference. It will also depend on what apps you are recording.

If you are worried about it take it to an Apple store. Personally I don't think anything is wrong unless it has to shutdown.