Video Stutter With Multiple Logged-In Users I'm experiencing significant video playback stuttering when there are other users logged in in the background via Fast User Switching. I'm not sure if this is do to a recent change to my user setup, or Lion, or what.

I've used Elgato's EyeTV software as my home DVR for 6 years, with the now-discontinued EyeTV 500, through a wide variety of updates, always without major problems. This was the first place I noticed video problems, so I initially suspected a software incompatibility. However the problem has also affected DVD, Netflix (Silverlight), iTunes (h.264) and Flash video playback.

In upgrading to Lion, I decided to do a clean install onto what had been the DVR drive, while keeping my Snow Leopard install around for a bit. After I was happy with the migration, I turned what had been the Snow Leopard drive into a DVR drive for EyeTV. However instead of running EyeTV under my only user, as I had been, I set up a new user, with the idea being:


My wife wouldn't need my admin account's password to watch shows she wanted to record
We wouldn't have to toggle audio settings back and forth when running video to the living room (my user would stay on headphones, this media user would stay on toslink out)
The media user could be set to automatic login without a password, so if power was lost when we were't home, when it came back, the DVR would come back too


Unfortunately what's been happening consistently is that if my admin user is logged in, with a few things running (nothing crazy, Mail, Chrome, iTunes, iPhoto, Terminal, etc.), video becomes unplayable, with whatever app that was doing video playback getting the Rainbow Wheel of Death every few seconds and lasting for several seconds.

I'm not sure if this is related, but if both users are logged in, the Lion login/user switching screen itself becomes nigh-unusable, possibly requiring multiple forced sleeps to figure itself out.

At this point I don't know what the problem is, although I have some guesses:


I can't have two users with conflicting sound output settings logged in at once (this is what I'm going to try first)
The media user needs to have admin privileges
There is some bug in Lion (unlikely, but I can't isolate this variable since I added the user at the same time as I upgraded).


Any ideas?
I experienced a similar problem with a 2012 MacBook Air with two users logged in. Both users logged in, stuttering video via AirPlay, OS X 10.8, 8GB RAM, plenty of room on the SSD. When using an iPad or iPhone on the same wireless network and AirPlay, no stuttering.

Logged out the second account, no stuttering.

I haven't solved any of your other issues, but did confirm the concurrent login problem.