[FFmpeg-user] inserting / embedding a thumbnail as cover art to an mp4 file

[S M]

Hello,
I used this command to generate thumbnails of all my mp4 files in a
directory
for %i in (*.mp4) do ffmpeg -i "%i" -vframes 1 -an -s 300x300 -ss 10
"%~ni.jpg"

But now I would like to embed those thumbnails into the .mp4 files as cover
art.
I know I can do it file by file using mp3tag, but is it possible to run a
command for a whole folder of .mp4 files?
I'm on a win 10 or win7 box.

Cheers
Scott