4K playback requires sustained data throughput, not just a brief speed-test peak. Bitrates vary by platform, encoding, and title, so this page does not give an unverified fixed bandwidth threshold. Check the platform's current official guidance, then see whether playback maintains the quality you want, buffers repeatedly, or takes time to recover after seeking.
Dolby Vision is not simply an option that appears when bandwidth is higher. The title must be available in that format, your membership tier must include it, and your playback device, display, and app must support it. Browser playback may also be limited by the browser, operating system, or content-protection chain. If the app does not show the relevant format, check device and title requirements before investigating the network.
After connecting, start with the platform's automatic quality setting and let the player buffer before checking whether quality stabilizes at a higher level. If playback starts normally but buffers often later, pause other heavy downloads, keep the target region unchanged, and compare other available routes. A brief speed test on a computer does not represent sustained playback on a TV, tablet, or wireless network.
Evening buffering can also be caused by a weak local Wi-Fi signal, congestion on a shared network, or the content delivery route. Compare other websites on the same device; if possible, test both wired and wireless connections, then try other exits in the same region. Compare IEPL, relay, and direct connections by actual playback rather than assuming a route type guarantees a particular video quality.