"To be diagnosed with Obsessive-Compulsive Disorder, one must have either obsessions or compulsions alone, or obsessions and compulsions, according to the DSM-IV-TR diagnostic criteria. The Quick Reference to the diagnostic criteria from DSM-IV-TR (2000) describes these obsessions and compulsions:[2]
Obsessions are defined by:
Recurrent and persistent thoughts, impulses, or images that are experienced at some time during the disturbance, as intrusive and inappropriate and that cause marked anxiety or distress.
The thoughts, impulses, or images are not simply excessive worries about real-life problems.
The person attempts to ignore or suppress such thoughts, impulses, or images, or to neutralize them with some other thought or action.
The person recognizes that the obsessional thoughts, impulses, or images are a product of his or her own mind, and are not based in reality.
The tendency to haggle over small details that the viewer is unable to fix or change in any way. This begins a mental pre-occupation with that which is inevitable.
Compulsions are defined by:
Repetitive behaviors or mental acts that the person feels driven to perform in response to an obsession, or according to rules that must be applied rigidly.
The behaviors or mental acts are aimed at preventing or reducing distress or preventing some dreaded event or situation; however, these behaviors or mental acts either are not connected in a realistic way with what they are designed to neutralize or prevent or are clearly excessive.
In addition to these criteria, at some point during the course of the disorder, the sufferer must realize that his/her obsessions or compulsions are unreasonable or excessive. Moreover, the obsessions or compulsions must be time-consuming (taking up more than one hour per day), cause distress, or cause impairment in social, occupational, or school functioning.[2] OCD often causes feelings similar to those of depression."
That's all out of Wikipedia, but in my opinion, you should really go make an appointment with a psychologist, or possibly even one that specializes in treating and diagnosing obsessive compulsive disorders, to see if you really have one. From what you have said, though, it does sound like you have a light one, although you may just be a very driven person who is ambitious (hence the practicing until you achieve your goal) and you may like to stay organized (thus you like to organize your DVD's and might like to memorize little tidbits of knowledge like the dates/directors). I do the 'one item at a time of food' too, so who knows? I might share that OCD with you, XD. Anyways, don't work yourself too much over it unless all of your OCD's take over your life and you cannot go on without doing them.
But before you seek a professional for help ... Try to break past these habits that you've formed over the years yourself. If you are able to, then obviously, there's no problem, and they're just things that you PREFER to do rather than having to do them in order to go on with life. So really, try to buy a movie without memorizing the director today or tomorrow. Good luck!