I have been afflicted with a bug which manifests itself by suddenly slowing down playback of timelines which in the most part contain a single Multicam clip to a point where editing becomes extremely frustrating. My iMac is a late 2012,
with 1 gig graphics card, and 24 gig of ram. I am running a software raid 0 through a usb3.0 dock. The timeline is 1080p and so is the multicam clip but one of the angles is 4K. When the system is working well (all clips are PRORES LT) I can edit smoothly with no proxies but when it is playing up out of desperation I resorted to proxies which worked well.
I have tried all the commonly suggested solutions including a clean install, trashing prefs, Vram and Pram resets, plus following numerous rabbits down multiple holes, non of these measures gave me any lasting joy.
Today however in a fit of exasperation I decided to try a simple but very effective trick. I wish I could say that I had sat down and carefully reasoned it through, but no, it was the result of anger, prayer and frustration. I simply ejected the raid, swapped to another port and replugged it in and everything was fixed. I then swapped it back to the original port but now it kept working. YES!!!!! ....So I kept editing for sometime and got hit by the slowdown bug again, I tried the same method, but this time I plugged it back into the same port, and it fixed the problem again. So the ejecting of the dock and replugging fixes the problem for a while.
Why this works I will leave to minds smarter than mine but I am guessing that there is an issue with USB3.0 which is triggered by an unknown event. Any suggestions would be gratefully acknowledged.
In my numerous google searches I have found many references to this problem but no solutions which have consistently worked for people. I hope this post helps because it is an extremely frustrating problem which has caused me to loose huge amounts of editing time over the last year or so.
MY final suggestion is that perhaps except for very slow data rate requirements or unless you use SSD's ( I have very occasionally edited on a SSD and can't remember having a problem), USB 3 is best avoided for video editing.
I hope this helps those who have suffered the same bug.
Thanks for your reply . Is it a bug? perhaps not, but certainly others have reported experiencing sudden slowdowns, whether theirs is due to the same issue, is of course conjecture. Yes it might be the raid, Perhaps it's just limited to a particular chipset of a component of the the usb 3 dock. I would appreciate any one else who has experienced this problem to report what their set up is. I think your comment about the cache is worth pursuing but I don;t know how you would test for it.
I always switch off background renders. What ever the cause of this issue it defies all of the standard strategies in my situation at least.
It’s an older computer, check they health of your system drive. I have a 2014 iMac that jpretty much did the same thing. Turned out it was the drive. It pretty much stopped working altogether as I was running some diagnostics on it, nothing invasive.
I’m not saying this is your issue, only that it’s worthwhile looking into, just in case.