In the Settings tab under Network settings you can set how you want to upload and download videos. As video files are large and can take up a lot of your mobile devices network bandwidth, Upload and Download videos using your Mobile Network is disabled by default. You can also check whether you would like to watch videos using your mobile network.
In the Teams tab in the Cloud storage section you can download videos while connected to wi-fi network so that you can watch at a later date without worrying about network quality or data charges. This also insures you can watch without any concern for network quality or speed.