are 4k videos on youtube really outputting in 4k

Some articles claim that the terms '2K' and '4K' were coined by DCI and refer exclusively to the 2K and 4K formats defined in the DCI standard.

4096 × 1716 (CinemaScope crop, ≈2.39∶1 aspect ratio)ĢK distributions can have a frame rate of either 24 or 48 FPS, while 4K distributions must have a frame rate of 24 FPS.: §4.3.1 The resolution of the video content inside follows the SMPTE 428-1 standard, : §3.2.1 which establishes the following resolutions for a 4K distribution: : 6 This specification establishes standardized 2K and 4K container formats for digital cinema production, with resolutions of 2048 × 10 × 2160 respectively. In 2005, Digital Cinema Initiatives (DCI), a prominent standards organization in the cinema industry, published the Digital Cinema System Specification. While typically referring to motion pictures, some digital camera vendors have used the term '4K photo' for still photographs, making it appear like an especially high resolution even though 3840×2160 pixels equal approximately 8.3 megapixels, which is not especially high for still photographs.

The terms '4K' and 'Ultra HD' are used more widely in marketing than '2160p'. : 2 Several different 4K resolutions have been standardized by various organizations. The term '4K' is generic and refers to any resolution with a horizontal pixel count of approximately 4,000. 1.1 DCI Digital Cinema System Specification.

Are 4k videos on youtube really outputting in 4k