pasting an image (poster art) on a MP4 movie file

[jamesgee]

For years I've been posting a movie poster on movie files keeping the 1000 x 1500 ratio. But since I got the High Sierra it stretches the icon image as a square. How can I get it back to pasting the image as its actual size? I posted an example of the file with the stretched image

 

[fisherking]

For years I've been posting a movie poster on movie files keeping the 1000 x 1500 ratio. But since I got the High Sierra it stretches the icon image as a square. How can I get it back to pasting the image as its actual size? I posted an example of the file with the stretched image

https://forums.macrumors.com/threads/changing-folder-or-movie-icons-in-finder.2073889/#post-25190985