Mac Pro 5,1 Quicktime Player 4K Stutter

To my knowledge, Quicktime relies heavily on hardware based encoding/decoding. This means using Intel Quick Sync for H.264, which saves battery life and accelerates decoding on compatible hardware. Since it's a feature baked into the processor, there's no way to add that to your CPU.

This is not to say that your Mac doesn't have the bones to decode H.264 4K. It just needs to run the whole thing through the CPU without acceleration. Hence, you probably won't get flawless performance in an application like quicktime which is so dependent on hardware decoding. Useful for battery life, yes. Not useful for people with older, but still powerful Mac Pro's.

In IINA, hardware acceleration is optional. So it runs playback through software instead, which is no problem for your beast of a CPU.

Hope this helps!

Since Mac Users first started editing video on disks, Disk Drive speed has been an issue editors have had to deal with.

Have you tried checking your disk playback speed with this really handy Utility?

https://www.lifewire.com/blackmagic-disk-speed-test-4065592

available as a free download from the Mac App Store.

2160p is 3840x2160. The "p" refers to the vertical resolution of the frame.

Blackmagic's test is simulating ProRes, Cinema DNG RAW and 10-bit YUV video, each of which has relatively little to no compression. Therefore, the data rates required for each are much higher than H.264, a highly compressed format, which bytes n' bits is trying to play. Editing 4k in those formats could well saturate the hard drive config on his system, but the exported H.264 4K shouldn't be bottlenecked by disk I/O.

A RAID would serve you well. I have four Toshiba 2TB drives, which gets me more than 500MB/s in blackmagic's speed test. That's enough for 4K editing, even with multiple streams if it's compressed.

Your graphics card is probably fine, but if you wanted to upgrade, a RX580 would probably be great for final cut due to it's strong openCL performance.

What codecs exporting to? H.264? ProRes?

That display is telling you that drive is sometimes not fast enough to read or write 2160p at 50 frames a second. You are using 3480p, so the drive may indeed be a limiting factor for full-speed playback.

I think the test is intended to run by itself, not competing against your editing. it simulates an editing load all by itself.

So you're saying it's just one specific file that won't play smoothly in QuickTime player?

I have a 2009 (4,1) Mac Pro which I upgraded to run 5,1 firmware. Depending on the kind of raid you want to set up, you won't need any additional components other than the obvious additional hard drives.

My setup is a little unusual. I run a 2TB RAID 0 using the first 500GB of space on my four 2TB drives, as the first part of a hard drive is always faster than the space at the end, which is used only when the drive is near full. I then use the remaining 1.5TB of each drive to create a 4.5TB RAID 5. The reason I do this split setup is because RAID 0 is the fastest, but has no redundancy (one drive fails and you lose all your data), whereas RAID 5 is safe against a single drive failure but definitely isn't as fast. Read/write speeds are around 500MB/s for the RAID 0, and around 300MB/s for the RAID 5; you'd probably see better numbers on both because your WD black drives are much faster than my Toshiba P300 drives. So what I do is use the fast volume for video editing, then backup to the safety of my RAID 5 on off hours using Carbon Copy Cloner. I also store other stuff like photo libraries and archival stuff on the 5 since I don't need blazing fast read/writes to access them.

If you wanted to skip this kind of complicated setup, a RAID 0 with a backup drive would probably work pretty well for you. RAID 5 isn't possible anyway, using Disk Utility. You'd need a copy of SoftRAID. Really great software, but probably overkill for a first time RAID.

So in terms of actual hardware you'd need to acquire, you could buy as little as one or as many as three additional WD Black drives like the one you have. You should use the exact same model if possible for peak performance. Then once installed, a RAID volume can be created in disk utility. Definitely invest in a backup drive if you don't have one already.