Detecting Standard or High Definition in MP4 files?

I'm trying to set up a rule to apply a tag to an MP4 file depending on whether it is a high def or standard def video. When I review the file info for an MP4 file, I see an attribute for Dimensions that I thought I could use for the purpose. But going through the "Other" options available in Hazel, I don't see "Dimensions" or anything else that I could use to set up the rule.
Any advice is appreciated!
Any advice is appreciated!