What

If a post contains a video, and does not have a featured image set, could we use that video's thumbnail as the featured image?

Why

Currently if a user wants to add the video thumbnail as a featured image, they have to get their own screenshot or download the image somehow, whereas other social media platforms show the image nicely.

This is a request through a support interaction:
https://wordpress.com/forums/topic/feature-images-larger-when-i-click-on-a-post/page/2/?view=all#post-3867976

How

Not sure how on the technical end, but a skim through tutorials says there are plugins that handle this, so I know it's possible to automate it.

The idea would be:

• if the post does not have a featured image
• or other images (because who knows what you'd do with the logic there)
• get the video thumbnail as a featured image