New iMac + Lion + Video = Freeze – Updated

See an expanded version of this article on TidBITS.

I’ve generally been fortunate when upgrading to new versions of OS X, but this time I’ve been hit with a nasty bug, that’s already caused me to lose some work. I have a new 27″ iMac, purchased in early June. This computer worked fine under Snow Leopard, but once I installed Lion, I started seeing random freezes when viewing videos. The videos could be any kind – Flash, H-264 or QuickTime – and the freezes are mean: the entire screen locks up, except for the cursor, and, while sound continues if I have iTunes playing in the background, I can’t do anything else but a hard restart. Sometimes it simply freezes, and other times I get displays like this (this is a screen shot I took of a QuickTime Player window; my iMac froze when I tried to close the window):

When this happens, the following messages are written to kernel.log:

7/23/11 12:02:40.000 PM kernel: ** GPU Debug Info Start **
7/23/11 12:02:40.000 PM kernel: 0x00006740
7/23/11 12:02:40.000 PM kernel: 0x0000008f
7/23/11 12:02:40.000 PM kernel: 0x00000001
7/23/11 12:02:40.000 PM kernel: 0x00000018
7/23/11 12:02:40.000 PM kernel: 0x0000a880
[and so on for a few hundred lines]

There’s a pretty long thread on Apple’s forums of people confirming that they, too, have this problem, and there are other threads discussing it as well. I called AppleCare on Saturday, and the technician was not aware of this problem. I told him I knew he wouldn’t have a solution, but wanted to make sure that the information got to Apple’s support technicians so it would go up the chain.

For now, I avoid watching any kind of video on my iMac. My MacBook Air has no problem, so I use that. But this is a disturbing problem, clearly related to Lion, which will hopefully be fixed in the first Lion update, which is likely to be released this week.

Update: I got a call back from an Apple technician this afternoon, asking for more information, logs, system profiles, etc. So I can confirm that Apple is indeed looking into this. It was relatively easy to reproduce the problem while on the phone with the technician, alas.

Update 2: The Apple technician has had me try a number of things to eliminate various possibilities – removing certain caches, etc. So far, none of them has led to a solution. The Apple forum thread is getting longer…

Update 3: The Apple technician asked me to test my Mac without the third-party RAM I had added. It froze pretty quickly. But while I was at it, I tried removing the original RAM, and was unable to make it freeze, no matter what kind of videos I viewed, even with many at a time. This may therefore be the culprit, even though a number of people on the Apple forum tested their RAM and found no problems with it.

Update 4: I just had a freeze, so it’s not the RAM. Too bad; that would have been an easy solution.

Update 5: I’ve been working with an Apple engineer for the past week, and he had me try everything suggested in this very long therad. He also asked me to do a clean install on a different disk, which I did yesterday. I was unable to reproduce the problem, despite running lots of videos, sleeping often, etc. This doesn’t mean it won’t happen, but I was able to easily reproduce it on my main boot partition.

There are certainly many variables – the clean install had no third-party sofware installed. But given the number of people posting here, I doubt that there’s any third-party software responsible. (Also, the Apple engineer has seen my crash logs, and hasn’t suggested that any specific software could be responsible.) So I’m a bit flummoxed by this latest development…

Update 6: I was able to get a freeze on my clean install. So that rules out any issues specific to my installation, third-party software, etc.

The story so far: Let me summarize the problem here, and discuss the many solutions proposed on the very, very long Apple forum thread. Viewing videos of any kind cause freezes. This doesn’t happen every time one views a video, and only happens after an iMac has been put to sleep at least once, or, in some cases, multiple times. These videos can be Flash, H-264, or QuickTime formats, and viewing may occur in Safari, Firefox, QuickTime Player, iTunes or any other program.

Doing the usual troubleshooting steps, such as resetting the PRAM or SMC does nothing. Doing a clean installation of Lion, with no third-party software installed, does not solve the problem. Deleting and/or reinstalling Flash has no effect on it. RAM or other hardware has no effect, though it may turn out that this is a hardware problem with video cards. (This seems unlikely, because many people with this problem, including myself, had their iMacs with Snow Leopard, and did not have freezes.) In short, none of the “solutions” offered on the Apple forums resolve the issue, as you can see in the trials I carried out in my various updates above.

For now, all we can do is wait on Apple. I’m willing to give Apple a bye on this for now, but this is starting to become a long time since the discovery of this issue. I can understand the anger of some users, and I’m a bit surprised that Apple didn’t discover this. However, it’s entirely possible that they didn’t have the new iMacs any earlier than users did for testing. (Which is, of course, reprehensible.) While some posters in the Apple forum thread mention similar problems with MacBook Pros, it is not the same problem; iMacs freeze; MacBook Pros seem to have kernel panics, and it seems to be a much more isolated problem.

In any case, I’ll continue updating this post as I get more information.

Update 7: I got some interesting information from someone who knows a lot about graphics cards and drivers. One of the most interesting things he said was that the number of background processes running may have an effect on this issue. This is interesting, because when I tried reproducing it on a clean installation, with no third-party software installed, it took quite some time to induce a freeze. On my normal installation, it’s much easier to reproduce the problem, and I do have a lot of third-party software installed that runs background processes. Nevertheless, this does not offer a solution to the problem, and Apple has still not come forth with anything. This is starting to become a bit long. Sigh.

Update 8: On August 16, Apple released Mac OS X 10.7.1, a small update which claims to “Address an issue that may cause the system to become unresponsive when playing a video in Safari.” It’s not clear whether this resolves the current issue. In my initial tests, I was unable to get my iMac to freeze, though I was seeing some artifacts when starting to play videos using QuickLook. It will take a while to be certain whether or not this resolves the issue. If anyone reading this has applied the update and is still having the problem, please post a comment.