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What is 2K Resolution?

2K is a label for video frames roughly 2,000 pixels wide. In digital cinema it refers to the 2048×1080 image container defined for DCI distribution; elsewhere it is also used for 1920×1080 HD and for 2560×1440, so the label alone does not fix the frame dimensions.

How 2K Resolution works

“2K” is a width class, not a delivery specification. In the DCI Digital Cinema System Specification, a 2K distribution is one whose image container is 2048×1080, a shape of about 1.90:1, compressed with JPEG 2000 and carrying 12-bit X′Y′Z′ color components. The container is an envelope and not a required picture size: the master’s picture files hold only active pixels and may not be padded out to the container. FFmpeg’s named sizes reflect this with 2kflat at 1998×1080 (1.85:1) and 2kscope at 2048×858 (about 2.39:1) beside 2k at 2048×1080. Outside cinema the label is looser. HDTV under ITU-R BT.709 is 1920×1080 at 16:9, which a Japanese communications ministry resolution table labels 2K, while YouTube’s upload guidance uses 2K for 2560×1440 and calls 1920×1080 HD.

Key facts

  1. A 2K cinema deliverable does not necessarily have a 2048×1080 picture. 2048×1080 is the DCI image container; the picture occupies only its active pixels, and the DCI master may not be padded out to the container. FFmpeg’s named sizes cover three 2K frames: 2kflat is 1998×1080 (1.85:1), 2kscope is 2048×858 (about 2.39:1), and 2k is the full 2048×1080 (about 1.90:1).
  2. 1920×1080 and 2048×1080 have different shapes (16:9 versus about 1.90:1), so converting between them forces a choice. Placing 1920×1080 unscaled in a 2048×1080 frame leaves 64 blank columns per side (39 per side in the 1998×1080 flat frame); scaling it to the full 2048 width gives 2048×1152 and requires cropping 72 lines; stretching it to fill widens the picture by about 6.7%. In the other direction, 2048×1080 fits 1920×1080 by cropping 64 columns per side or by scaling to about 1920×1012 with letterbox bars. This is frame arithmetic, not cinema delivery guidance: because the DCI master may not be padded out to the container, ask the recipient which picture size it expects for a 16:9 film before adding bars.
  3. Matching the 2048×1080 raster does not make a file a digital cinema deliverable. The DCI specification also requires JPEG 2000 compression and 12-bit X′Y′Z′ color components, so an H.264 or HEVC file at 2048×1080 shares only its dimensions with a DCI 2K distribution. The 2K label itself fixes no codec, color encoding, frame rate, or bitrate.
  4. On YouTube, 2K means 1440p: its guidance lists 2560×1440 as 2K and 1920×1080 as HD, includes no 2048×1080 entry in its 16:9 list, and advises against adding padding or black bars to an upload. For that destination, keep a 1920×1080 source at 1920×1080 instead of padding it to a cinema raster.

When 2K Resolution matters

The term matters whenever a brief or delivery specification says 2K without giving pixel dimensions. Ask for the exact width, height, and picture aspect ratio before scaling: a cinema request may mean 1998×1080 or 2048×858 inside the 2048×1080 container, while a streaming or broadcast context may mean 2560×1440 or 1920×1080.

How Transloadit helps with 2K Resolution

Transloadit’s /video/encode Robot sets output dimensions from explicit width and height values and a resize_strategy, so the Assembly Instructions state whether a 2K target means 2048×1080 or 1920×1080 and whether a source with a different shape is padded, cropped, or stretched.

The documented default strategy is pad, which scales the picture to fit while preserving its aspect ratio and fills the remaining surface with a background color; fillcrop preserves the aspect ratio but trims the excess, and stretch ignores the aspect ratio. zoom is on by default, and its effect depends on the strategy: by these definitions a 1920×1080 source already fits a 2048×1080 output at its own size, so pad keeps the picture at 1920×1080 and fills the remaining 128 columns of width. Setting zoom to false stops smaller videos from being stretched to the requested width and height; under pad they are then centered with background on all sides. The documented video presets produce formats such as MP4, WebM, and MPEG-TS and include no Digital Cinema Package preset, so treat a 2048×1080 output from a preset as a video file with 2K dimensions, not as a DCI deliverable.

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