4K Blu-ray Still Outperforms 4K Streaming, Says Engadget

The key factor is bitrate, which measures how much data a video uses over time. Ultra HD Blu-ray supports maximum video rates of 108 Mbps on 66GB discs and 128 Mbps on 100GB discs, according to the Blu-ray Disc Association. Internet streaming, by contrast, is built around adapting to network conditions. Apple's HTTP Live Streaming provides multiple bitrate versions so playback can switch as networks change, and Netflix recommends at least a 15 Mbps connection for 4K, though that is a connection speed recommendation rather than the actual video bitrate.

Compression artifacts become more visible when data is insufficient. Film grain, fast motion, and fine textures require more data, and grainy footage can show blockiness even at bitrates that are excessive for simpler animation. Banding, where smooth color transitions break into visible steps, can also appear in dark scenes.

The report notes that higher bitrate does not guarantee a better image, and a poorly encoded disc can look worse than an excellent stream. However, when source material and encoding quality are comparable, more data means less visual information is discarded.

Some high-bitrate streaming services narrow the gap. Sony Pictures Core's Pure Stream mode runs between 43 and 80 Mbps and requires at least a 115 Mbps connection for the highest setting. Sony says this tier delivers an experience comparable to 4K UHD Blu-ray. Local streaming through personal media servers like Plex can also send files in their original form via Direct Play or repackage them without recompressing the video, avoiding additional quality loss.

Engadget concludes that the real issue is not whether a movie comes from a disc or over the internet, but how much picture information actually reaches the screen. While exceptions exist, mainstream 4K streaming still lacks the data capacity that Ultra HD Blu-ray provides.