I have an Intel iMac from a few years ago. And I connected a USB-C external hard drive to it. Plugged it into the back of the computer and velcroed it in place as Mr Sparky has discussed 
Problem is when I play a video file off it, it stutters. So I imagine either the drive itself or USB-C isn’t fast enough to play video off.
Do I need an SSD drive? Or do I need a thunderbolt drive?
Thank you in advance for any assistance!!
4K or HD? Format? Codec? What speed are you getting from it? You can check it with Blackmagic Disk Speed Test im Mac App Store
Have you tried using a different video player? VLC has been a favorite for years.
If it‘s a mechanical hard drive, USB-C is very unlikely to be the culprit (you‘re using the cable that came with the drive, aren’t you).
Yes, mechanical drive. One possible factor:
I created encrypted disk images on the drive. So I double click, it opens the disk image with the password saved locally. All very quickly. I would assume this shouldn’t impact playing speed. But I dont know if maybe when I decrypt the disk image, it only decrypts the file names instantly? And then it decrypts the video files themselves in real time?
These aren’t huge files, like 720p even causes a problem.
Hi,
Even high bit-rate 4k video is only about 85 Mbps.
USB 2.0 spec is 480 Mbps, whilst 3.0 ups that to 5,000 Mbps so they wouldn’t be the culprit unless you have a faulty cable or something.
A mechanical HDD should get over 800 Mbps.
So, the problem is likely to be, I think:
I suggest starting with changing the cable, if that doesn’t help then try right clicking on the file in Finder and choosing to encode the video from the Services menu, and try playing the result using QuickTime Player.
By the way, have you tried copying the file to the internal drive and playing it?
That suggestion of running Black Magic was also good.
Check the drive speed. Once on the drive, once in the encrypted volume. The difference might point towards the problem.