You need to have a strong internet connection to complete the video screen. Please find a strong connection, if you are on your phone please ensure you are on WiFi.
Also, make sure you don't have anyone streaming videos while you are trying to complete your video screen.
Downloading the video for you to watch doesn't require too much bandwidth, but when you try to push your video back to us; that is what requires a strong connection.
Tip: Libraries generally have rooms you can use as well as strong WiFi. If your home connection isn't strong enough consider going to the library.