YouTube Fullscreen Choppy Playback with mid 2011 iMac

I'm looking at all the solutions, so far the solution about leaving "about this mac" window open seemed to work for me.

yep, tried everything

even tried a clean OSX install, still happens.

I tried that. I tried that many times. I used to tell people to do that before getting my new Mac with Snow Leopard a couple of weeks ago. But still I had choppy full screen video.

I just deleted those folders, and bam! videos now run smoothly. I didn't even need to reinstall Flash.

I was about to give up and switch to Firefox, which for some reason was immune to this flash problem.

David M Brewer wrote:

EeZeEpEe wrote:

SUCCESS! Finally! After all these months of command-scrolling to zoom in I finally have it running smooth. I think what really did it was I opened up ~/Library (User library), typed "flash" in the search box, clicked "library" so it would search only there, then deleted the two "Flash Player" folders. One was cache and another was preferences. I did do the uninstall and reinstall too but I'm guessing this was the really fix.

You can remove those files by doing this:

Open Systems Preferences...

Click on the Flash logo in Others...

Click on the Advance tab...

Browsing Data and Settings...

Click on the Delete All button...

I went through the same process as the rest of this thread's readers...toggle hardware accel, manually deleted "~/Library/*...*/Flash Player" folders, produced one smooth play, although in fullscreen frame rate was inconsistent. After refresh, video reverted to unwatchable state...toggle hardware accel again, no difference. Cleared all caches through the preference pane, same result.

I considered the "About This Mac" workaround for a bit, pondering perhaps some fault within the interaction between flash, cocoa, and whatever other abstraction layers separate flash from the integrated gpu drivers in my 15" retina mbp (flash in safari doesn't trigger a switch to the discrete gpu).

Then it occurred to me that Adobe has had its dev fails in the past (ahem...photoshop being 32bit because of carbon until CS5), but they already acknowledged this issue and fixed it once before - not sure if those release notes were from this . It would make sense that, if the issue resurfaced, they'd be doing something to fix it.

By that logic, I downloaded and installed the Flash Player 11.8 Beta. Immediate improvement, especially once I re-enabled hardware accel. Multiple refreshes, cmd+Q and restart safari, reboot the whole computer...rock solid all day long. Not even an intermittent wifi connection with reception bordering between meh and outright connection fail was able to impede the performance.

So thats my suggestion - install the latest flash beta.

Hmmmm. Tried installing the Flash beta 11.9 and I still have this problem. Frame rate is a little better then before but still unwatchable and nowhere near non-full screen frame rate. This is super frustrating. I bought the big video card at the time to avoid these kinds of problems.

For reference this is my system info:

iMac 27" mid 2011

3.5 GHz Intel Core i7

24GB 1333 Mhz DDR3

AMD Radeon HD 6970M 2048 MB