This refers to full-length feature films compressed down to roughly 300 megabytes. In standard formats, a 1080p Blu-ray rip can easily range from 2GB to 10GB. Compressing this down to 300MB requires aggressive optimization.
Large 4K TVs, where you will see "blocks" (artifacts) in dark or fast-moving scenes. 📱 Draft Guide: Preparing Your Portable Library 1. Optimization (DIY Compression)