If exam videos are not displayed in sufficient quality in FahrAPP while you're on the go, you can download them in advance in your Wifi

Download the videos in "high quality" in the cache management settings at home using Wifi. You can find the cache management in the main menu > Settings (Gear symbol top right) > cache management. 

If you have a fast internet connection you can stream the videos by deleting low quality question pictures and videos from the cache management.