Understand 4K resolution, codecs, and containers
High-resolution adaptive formats often separate video and audio into DASH streams. The server downloads the chosen representations and muxes compatible tracks into the requested container while preserving their compressed bitstreams when stream copy is possible. Choose H.264/AAC MP4 for broad device support when available; choose VP9 or AV1 only if the playback device supports them. 2160p60 and HDR files can be very large, so storage, network speed, and playback hardware affect the experience. The source's original encode—not the container label—sets the maximum detail.
4K YouTube video is commonly labeled 2160p and contains substantially more pixels per frame than 1080p. The source may publish UHD as VP9 or AV1, often in WebM, and some videos also expose MP4 tracks. MP4 and WebM are containers; they do not guarantee H.264, VP9, or AV1 by themselves. YTMetadata lists source formats that are available for the link and does not upscale a 1440p or 1080p upload into genuine 4K. Codec, frame rate, and HDR support can vary between videos.