+1 to MrC again. Here is my smartlist (called Missing Video Thumbnail) which is exactly what I was after:
[Thumbnail Offset Small]=0 [Media Type]=[Video]
Had reason to do exactly this process and thumbs up to Interact for storing the answer. Nice work MrC and jmone.
As a follow up, what was not clear to me here is that [Thumbnail Offset Small] is a hidden Library Field. So, when I set up a smartlist in simple user mode, this item doesn't show in the standard Rules to choose from. There's a story behind this.
Might not be news to anyone else out there but I wasn't sure whether I need to set up a new field to make this work. I navigated to:
Tools > Options > Manage Library Fieldsand when I poked around I found that the Fields drop down has an option:
Show all fields (including hidden fields)and sure enough, our little friend was there.
So, I just brought up the edit dialogue for the missing thumbnails smartlist and clicked on the Import/Export button in the bottom left and copy/pasted in the expression string. OK'd out and ran the list. Worked a treat..