Choosing thumbnails in iMovie Projects

Your observation is correct. The selected thumbnail will not carry over with the method that you used from the Get Info box.

iMovie has no feature to select the thumbnail. iMovie chooses the thumbnail from the center point of the movie. Try throwing in a black background of suitable duration at the end of the movie to change the center point. Unfortunately, it will be difficult to pick exacty the frame that you want as the thumbnail, but at least the thumbnail might be a better selection than the original one picked by iMovie.

-- Rich

First of all make a .jpg etc. of the picture you want as the poster frame.

Then export your movie and of course it will have some random frame which you don't want.

Do not fear . . . right click on your exported movie, select "Get Info" and you will see this window.

Drag and drop your selected picture onto the little image at the top left and it should change into your desired thumbnail.

By "ATV" do you mean Apple TV, as in the physical device?

I do have an Apple TV, but never actually copied video files over, I use it to run apps or to use with Airplay.

I can, however, tell you how to add a specific thumbnail to a movie in the TV app on the Mac. I expect that if you then access it from there on the Apple TV device, it will use that thumbnail, but I have not actually tried.

In the TV app, click the ... button next to the movie and choose Get Info; Click on Artwork, then click Add Artwork button; navigate to the desired image file and click Open.

I hope this helps. If it does, credit should go to Ian, who drew attention to this question on FCP forum.