Performance issues with MKVToolNix Gui

Hello, I often split and merge large mp4/h265 Files, and I always wondered why the progress is “slow” for splitting without reencoding.
Slow is relative in my case :wink:
I use a PCIE4.0 NVME SSD which is capable of 6000MB/s read and write. ATTO Disk benchmark verifies that the SSD is really working at this speed.
I did some testing with a 45GB File to measure times:
copy&paste in the same folder: 13Sec
MKVmerge without timestamps, just write the entire file: ~70sec
Shutter Encoder write without changes: 27sec (for comparison)

Task manager shows me SSD Usage of ~800MB read and write, so the drive isnt really under load. But I saw that CPU usage, while at 10% in total, is at almost 95% at one single core while all other cores are mostly idling.

Could it be that MKVToolNix Gui is not multithreaded and generates a bottleneck while the SSD would be capable of much more?

Thanks in advance!

MKVToolNix is indeed not multi-threaded, and even with only a single thread it isn’t really super efficient wrt. to memory transfers. This is known & will not change as all low hanging performance fruit have already been picked. Any further substantial improvement would require a huge amount of work, which I’m not willing to invest it.

Ok, many thanks for your quick response!