Improve video poster image handling

[westonruter]

• Ensure poster image is centered in editor as it will be on frontend.
• Make sure video is displayed instead of poster image.
• Add warning when no poster image is selected.
• Show preview of poster similar to how is done for the featured image.

Fixes #2214.

No Poster Image Selected

Poster Image Selected

Video Plays in Editor

[swissspidy]

I added a small change to automatically use the video's featured image as a poster if there is one. This reduces the likelihood of getting the warnings.

I also simplified the UI a little bit, there were too many elements to do the same action IMO.

Screenshots:

[westonruter]

I added a small change to automatically use the video's featured image as a poster if there is one. This reduces the likelihood of getting the warnings.

Doesn't this run the risk of setting the poster to be totally unrelated to the video?

Oh, I misunderstood. The video's featured image:

I wasn't aware that this was normally a thing.

[westonruter]

I also simplified the UI a little bit, there were too many elements to do the same action IMO.

Sure. But just to note that the elements I added were the same as for the featured image control.