Welcome to the forum.
[Soapbox Mode ON]
I find that iTunes (and its companion Apple's QT Player) can cause all sorts of problems, and one is that there are a bunch of other "things," that get loaded, which will launch at bootup - mainly "helper" applications for iTunes, and those are unnecessary for general computing, plus steal many CPU cycles, and resources, when one is editing Video. I just go into MSCONFIG and turn those "helpers" OFF, then reboot. The only one that I found necessary was Bonjour Services, which was also needed by my font manager, on my workstation. I could turn it (plus others) OFF on my laptop.
QT Player can also "seize" many File Associations, for itself, and that messes things up for other programs. It has gotten a bit more benign, from its earlier rogue behavior, where, by default, it just set all File Associations for itself - even ones that it could never work with, like DOC, etc.. Better, but still not perfect.
That is why I always hesitate to update iTunes, on my laptop, and when I do, I always do a System Restore Point, for before the update. Also, I find that most updates to iTunes adds more "glitz" to the GUI, but removes useful features. I am about 6 updates behind, and wish that I had not done the last one, that I did. Though I have not had any issues (still turned OFF most of the "stuff"), the GUI is now less useful to me, than the previous one was. Should have tested, and then used my System Restore Point.
Not sure if it's as bad on the Mac side-of-the-street, but for the PC, I feel that Apple just adds a bell, a whistle, and a little dog in a tu-tu, doing useless tricks, while they remove three good features.
[Soapbox Mode OFF]
If you do have a System Restore Point, from before that update, just do another, for today, then boot to Safe Mode, choosing to use that earlier System Restore Point, reboot when told to do so, then test. At the worst, all you have lost is a bit of time, as you have today's System Restore Point to go to, if things do not improve.
I would agree with Bill on this this one, to the point that I'd recommend not installing iTunes at all on a production rig. You should install only those programs which you need for editing, and install stuff like this on a separate computer.