Shell – PowerShell command for ffmpeg to process items in a folder recursively

I'm trying to figure out what PowerShell command [or script if necessary] might allow ffmpeg to recursively traverse a directory, pull stills via the -vf flag, and put all the stills into a folder without any filename conflicts that would cause overwriting.

So I know that this works fine for an individual file:

ffmpeg -i input.mov -vf fps=10/60 still%04d.jpg

The files generated start from still0001.jpg and count up to still0002.jpg, still0003.jpg, etc.

I have a directory that looks like this, with video files at different levels:

• topFolder1
  • midFolder1
    • video1.mov
    • video2.mov
  • midFolder2
    • video3.mov
    • video4.mov

I'm trying to use a PowerShell command that can pull stills from all the videos video1.mov, video2.mov, video3.mov, and video4.mov and drop them into one folder.

I found a PowerShell command that purports to have ffmpeg traverse a directory recursively, but when I try to adapt it, it's not working.

I run:

PS T:\Exports\1 - Dailies\stills test> for /F "tokens=*" "%G" IN ('dir "T:\Exports\1 - Dailies" *.mov') do ffmpeg -i "%G" -vf fps=10/60 still%05d.jpg

But I get this error:

At line:1 char:4
+ for /F "tokens=*" "%G" IN ('dir "T:\Exports\1 - Dailies" *.mov') do f...
+    ~
Missing opening '(' after keyword 'for'.
    + CategoryInfo          : ParserError: (:) [], ParentContainsErrorRecordException
    + FullyQualifiedErrorId : MissingOpenParenthesisAfterKeyword

Where am I going wrong?