FIXING A LAGGY / SLOW LOADING OSX 10.9.X - 10.10.X
Hey,
in case anybody else experiences a very bad performance/a two-minute lag in OSX 10.9 or higher, if 1.) a audio player app will open or 2.) safari will be opened will a graphics rich webpage, then I guess I have found the cause of this:
Safari and also audio apps that are compatible with audio components ( audiounits, in /Library/Audio/Plug-Ins/Components ) will utilize the system component “com.apple.qtkitserver.xpc”. You can see this xlc service as a process in the activity monitor, one of the rare processes that still use 32bit emulation mode…
qtkitserver.xpc seems to be a relict of quicktime and is responsible for those finder movie previews, if you press the play button in the icon or use quicklook. It utilizes all audio components (I don’t know why…). To make sure that you have the same problem, enable a spy session with fs_eventer or the freeware “filemon”:
In new terminal window just write:
sudo fs_usage
sudo fs_usage | grepComponents
Look for intensive scanning of audio components. Surely you even can filter the output in a more sophisticated way, but I have no clue about terminal commands…
Freeware filemons for OSX:
fswatch- install with “brew install fswatch”, terminal command
fs_usage - default system installed
Filemon - frontend for fs_usage by Deep-IT.ru 
fseventer - Very sophisticated freeware frontend view (but useless?) by fernlightning, grab it here before it will be deleted! Vendor shut down webpage.
So if you asking me if this could be a solution to fixing a slow mac osx, look into activity monitor if there is a process opened “qtkitserver.xpc” in 32 bit, if you open safari and experience a system slow down.
EDIT: See solution 4 below.
EDIT 2: Solution 1 works! You only need to restart the system one time!
Solution 1
My current solution is to completely disable this process by renaming the file. In terminal type:
sudo mv /System/Library/Frameworks/QTKit.framework/XPCServices/com.apple.qtkitserver.xpc /System/Library/Frameworks/QTKit.framework/XPCServices/com.apple.qtkitserver.xpc__
Now restart Safari. The speed-up is impressive. Almost every tool and especially browser and audio apps will load so fast now! The drawback of this method is that you will loose video previewing in finder (I never use it). Quicktime codecs, Final Cut etc. will still work! EDIT: Also icon previews of videos and quicklook videos.
On some webpages html5 video may be broken until next reboot. So do a reboot now.
Solution 2 (not approved)
Another approach is to rebuild the xpc cache in OSX. This seemed to speed up things a bit, but not as fast as the first method:
sudo /usr/libexec/xpchelper --rebuild-cache
Don’t know if this approach will fix the problem permanently.
Solution 3 (not tested)
There is also a switch for LaunchDaemons available:
<key>EnvironmentVariables</key>
<dict>
<key>XPC_SERVICES_UNAVAILABLE</key>
<string>1</string>
</dict>
Maybe it could help if this option would be added to the system agents “quick look” and “webkitplugin agent”…
Addition: Disable symbol preview in Finder
Also disable any icon previewing in the Finder in places where videos are stored: Go to root level, right click in “Applications”, “Library”, “Users” and on “view options” in context menu. There, disable “symbol preview” and save as standard. Repeat this for all download dirs, system’s movies dir etc.
EDIT:
At least do solution 1+2 +addition… Man, I got my OSX back! The system is so fast now.