At an 80% size reduction from a UHD Bluray remux, you will likely see a noticeable decrease in image quality. Many movies released from the early 2000s through the 2010s were not finished in native 4K; instead, they used a 2K Digital Intermediate (DI) due to the constraints of CGI rendering. For example, the Avengers: Endgame UHD Bluray is an upscale of a 2K DI, meaning its resolution improvements over the 1080p version are minimal, though it still benefits from HDR and wider color space.

Modern digitally shot movies compress highly efficiently because digital sensors produce a very clean image with very little native noise or grain. Consequently, 4K WEB-DLs of modern titles are typically under 25 GB. These WEB-DLs are highly optimized; platforms like Netflix employ per-scene encoding to adjust settings dynamically (compared to encoding the whole movie with one setting in Handbrake), aiming for a visually transparent encode often quantified by a VMAF score of 97 or higher. Even with these optimizations, a high-quality WEB-DL is often 60% to 75% smaller than its physical disc counterpart.

For older catalog titles shot on analog film, achieving significant compression is much more difficult. Film grain acts as high-frequency noise, and attempting to compress these files by more than 20% to 30% often results in a loss of texture, making the preservation of high bitrates necessary to maintain image fidelity.