New options are rolling out in the YouTube app for Android and iPhone users to provide more control over how you see your videos. Until now, the resolution defaulted to an Auto setting based on your connection, with the option to manually select from the maximum value (mostly 720p or 1080p) down to 144p.
The latest version of the app now gives two additional options for setting the resolution. The higher picture quality selection prioritizes image quality to the best possible option (up to 720p) while the data saver option limits the quality to a maximum of 480p to save you from using all of your data while streaming.
The settings can be made per video, by selecting Quality from the options menu. You can also make universal changes from the video quality preferences in the YouTube settings menu.