Can’t be done in PDF any way I know of. There are tricks for doing it in
EPUB and DPS.
Two unproven ideas (never done that myself):
You could also superimpose your round frame as cropping mask into the movie - maybe in Premiere?
I meant to place the individual frames as image rather than as movie.
It's possible to put a movie into a round (or rounded cornered) frame. (Or make it look like it is.)
Put the movie on the page.
Create a rectangle with a Paper color.
Create a rounded object inside the rectangle.
Compound these two paths.
Make them a button that plays the movie.
Position over the movie.
Correct! Good solution!
But you missed a couple steps in your directions:
(1) Make a rectangle filled with Paper color.
(2) Make a circle filled with None (this will be the mask for the movie).
(3) Move the circle over the rectangle. Select both and choose Object > Path > Make Compound Path. This creates a paper-color rectangle with a hole.
(4) Position the rectangle-with-hole object over the movie to position the mask.
(5) Use the Buttons and Forms panel to make that object into a button. Give it an action of playing the movie.
(6) Choose File > Export > PDF (Interactive).
It works because the button (which has interactivity) is atop another object which has interactivity (the movie).