The GDC clip is basically him talking on others people work completely unrelated to what he's supposed to sell. High five!
LibGDX Tutorial: Dealing With Multiple Device Resolutions
Learn about how to work with multiple resolutions as aspect ratios using Viewports and Cameras in LibGDX. It describes the many types of available cameras, rendering with a camera and setting your game world up to use your own coordinates instead of pixels.
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