Plenty of tools call themselves a 4K YouTube downloader and then quietly cap you at 1080p or re-compress the picture. Y-Download does neither. Paste a link and you will see every resolution the uploader provided – 1440p, 2160p (4K) and, on the few videos that have it, 4320p (8K) – each with its codec, frame rate and an estimated file size. The stream you pick is downloaded as YouTube encoded it and placed into an MP4 with the best available audio track. No re-encoding happens at any point, so the file is pixel for pixel what YouTube's player shows at that setting.
There is one thing to understand before you download: YouTube only encodes resolutions above 1080p in the VP9 and AV1 codecs, never in the older H.264. That is why a 4K download from any honest service comes as VP9 or AV1 inside the MP4 container. These files play in Chrome, Edge and Firefox, in VLC and IINA, on modern Android and iOS devices, on Windows 11 and on most smart TVs sold since 2020. The notable exception is QuickTime on macOS, which does not decode VP9 or AV1 – use VLC or IINA instead. Older Windows machines may need Microsoft's free AV1 Video Extension.
Frame rate is preserved as well. If the upload is 60 fps, the 4K stream you download is 4K60, labeled 2160p60 in the list. What Y-Download deliberately skips is HDR. YouTube's HDR streams use a wider color range that only HDR displays reproduce; on an ordinary screen, or in a player without tone mapping, they look gray and washed out, so we pick the standard-range (SDR) version of each resolution for consistent playback everywhere. Be honest about your display, too. On a phone or a 15-inch laptop, 1080p H.264 is indistinguishable from 4K and a fraction of the size; the 4K file earns its place on a 4K TV or monitor, in an editing timeline, or when you plan to crop and zoom.