You'll need to add thumbnails to your videos so that they are properly displayed in your catalog and as part of collections. You can find the settings to display your thumbnails under Videos>>Appearance.
If you want to check out some expert advice on making your thumbnails the best they can be check out our blog post on this very topic!
They'll look like this in your catalog:
Above is the Catalog Image.
You'll also need to set a Player Image which is what appears when someone clicks a video in the catalog and is taken to the content page like this:
This Player Image will be used for thumbnails of collection videos as well.
You can replace these images at any time for existing videos by removing the existing thumbnail and uploading a new one:
If you've swapped thumbnails and aren't seeing them right away just hang tight, occasionally CDNs that deliver the optimized images can be a little slow to update in certain areas of the world, but rest assured it will appear soon!