If you're anything like me, you like your iTunes library to look neat and tidy, and to contain all the information it's supposed to, even if your content didn't come from the iTunes Store.
For instance, in iTunes 11, the Description field for movies and TV shows became much more prominent. So prominent, in fact, that it purposefully points out that the description is missing if you haven't added one.
Short of describing movies and episodes of TV shows yourself in 256 characters, there's no way to consistently add the Description in. That is, unless you use MetaZ.
MetaZ is a new implementation of MetaX, a tagging program which stopped getting updated a while back. It allows you to load in any video file and update its MP4 metadata, which iTunes can then read and display.
Using MetaZ, metadata fields that aren't editable in iTunes can be edited and saved. For example, the Date field cannot be set in the Get Info panel in iTunes, but shows up when set:
You might be thinking, "Great, now there's even more data I need to find so that my iTunes metadata is complete!", and you'd be right. However, I haven't mentioned the best feature of MetaZ.
After importing a video file, MetaZ will automatically search Tag Chimp, TMDb and The TVDb to find the appropriate data for that file, including description, date and more.
Simply select a file in the right-hand pane, then once MetaZ has finished searching, choose a metadata source in the left-hand pane. The middle pane will then update with the data from your chosen source. Select the checkbox next to each item you wish to save. You can also manually make changes in the text fields if you want.
When you are finished editing, click Write in the toolbar and the metadata will be saved into the file. Once MetaZ has finished writing, iTunes should be updated automatically with the new data. I've shown the process here with a TV show episode, but the same applies for movies as well.