Not sure which or how many cores? On the PC I had the Performance monitor open so I could see all 24 cores/ 48 threads were in use and way more swapping going on and memory usage. I did have Activity monitor open and iStat monitoring (did I mention I had it hooked up to two 27' 4K monitors too?) The M1 Max showed 93% CPU usage but memory use was low. Not even in the ball park to how hot my 13' 2020 MBP i7 would get doing the same task and taking a lot longer. What was also impressive was the MBP was only slightly warm. Not totally scientific and as I said I am not at work so I don't have detailed stats but for me anything that shaves 5 minutes off is 5 minutes I am not having to wait.

Keep in mind Handbrake, if I am remembering correctly, installed using Rosetta.

It took 14 minutes on the M1 and 19 minutes on the PC to convert the MKV to an MP4.

Okay I am not at work now where I did this little experiment, but today I took a 1080p 105 minute 5.8Gb MKV video and ran it through Handbrake on my 2021 14' MBP M1 Max, 64GB and also on my Windows 10 PC - with 2970WX Threadripper, 64 GB DDR4, all SSD drives.

Apple m1 handbrake