Video thumbnails let your audience view a quick snapshot of your video. You can use the option Single automatically generates, or you capture or upload your own.
Add automatic or custom thumbnails:
Log in to your Single account.
From the left sidebar, navigate to Video > On Demand.
On the Manage Video On Demand page, select the video you want to edit.
Tap the "X" > Remove icon to remove the current thumbnail.
You now have two options to add a new thumbnail:
Upload a custom thumbnail.
Go to the video's preview page and tap 'Capture Thumbnail' to create one within Single.