I have a 2010 MacBook Pro with Core i5 processor.
I looked up my processor on Wikipedia. It has a frontside bus capable of 3200 megabytes per second. So when I convert a high-bitrate 1080p video to 1080p with lower bitrate, it takes many hours and the meaningful output is 1 megabyte per second or less. Why is that?
P
The processor will bottleneck at some point during the conversion process. That model did usually come with an extremely slow traditional hard drive so if you don't have an SSD that will be causing you a lot of lag.
Murzy
It may be swapping things in the background.
Marvinator
You are making a mistake when you read 3200 Mb per second as Megabytes. It's MegaBITS. Your processor is doing what it should, if you want faster, buy a new machine with a faster processor, AND more RAM and maybe an SSD.