Last resort data field cannot be read

[punchycool]

I have read the man page and tried many different examples, but am stuck. Thx for a great utility!
Most of my media files have the metadata tag "Date Created" or "Create Date" or "Date/Time Original". For these tags, I can easily read them and create filenames (and directories) commensurate for my needs.

But, some of my media files only have a "File Modification Date/Time" metadata tag which represents the timestamp for the file. There is no other date field to read from with the original file stamp. How do I access this field to read from it? These commands do not alter these files. Some of these files are AVI, but others are PNG or JPG.

exiftool '-filename<FileModificationDateTime' -d %Y%m%d%%-.4nc.%%le file.avi

...ModifyDate...
...ModificationDate...
...FileModDateTime...
...ModDateTime....

[punchycool]

Well, I figured it out. Sometimes writing it down generates other ideas.
The answer is:  FileModifyDate

This is what I was after:
exiftool '-FileName<FileModifyDate' -d "%Y%m%d_%H%M%S%%-c.%%e" .