Tags are available for most text and numerical fields and can be dragged from the tag cloud to the text fields. Multiple tags can also be combined in one files as shown in the screen shot.
For most tags you can select the source of the tag by clicking on the little triangle next to the tag.
Takes the field from the current metadata which is also displayed in the metadata sidebar.
Takes the data from the filename or file metadata. Most formats have very limited metadata available. For mp4/m4v files that were already completed with metadata all of these values are accessible.
When updating iTunes items, all metadata available in iTunes will be available here. You can use this as the source so that custom metadata in iTunes will remain intact when updating through iFlicks.
Additionally to the source of the metadata you can enable a bunch of modifiers for each of the fields
Capitalize first letter of each word.
Make whole text lowercase.
Make whole text UPPERCASE.
Strip everything after the last .
Clean text by removing special characters.
Make sure all numbers are 2-digit by adding a leading 0 if necessary.