February 9th, 2013
When you receive an email with an audio attachment (for instance, voice memos sent by 'Say it & Mail it' from your iPhone to your Mac as a .wav file), you would expect to see a QuickTime audio player that lets you play the audio.
QuickTime audio player in the body of your email.
Instead, you may see an icon like this which requires you to double click to open the QuickTime Player app. Or you may see an iTunes icon which requires you to double click to open iTunes.
com.apple.xpchelper.cache is missing from /System/Library/Caches/ . This can happen if you have cleared your cache folder. When you clear the cache folder, the com.apple.xpchelper.cache file is not being recreated as it should be (bug in Mountain Lion?)
You need to get com.apple.xpchelper.cache from /System/Library/Caches/ on another Mac or from your Time Machine Backup. Then drag that file into /System/Library/Caches/ on your Mac and reboot. Then Voilla! your QuickTime audio player is back in Mail.
xpchelper is the XPC helper agent.
XPC stands for "X Performance Characterization"
xpchelper performs services on behalf of the XPC IPC facility, where IPC stands for "Inter Process Communication" which refers to different programs or processes communicating with each other, usually requesting information.
It is a required component of QuickLook. You will notice that when the QuickTime audio player is missing from your mail, if you try to play the audio file using QuickLook, you will just get a blank window with a spinning wheel forever.
Restoring com.apple.xpchelper.cache fixes the problem.