You can easily preview an uploaded video from its Details page. Previewing your videos will allow you to make sure the correct video is uploaded before entering its details and publishing it to your catalog.
To preview videos:
Navigate to Content
Under the Videos view, find the video you want to preview, then click its 3dot button
Within the Details tab, you will see a preview of your video that you can interact with. You can also click the View on the Website button if the video is already published.