Understanding Aspect
Ratios & Delivery Specs
Frame sizes, containers, and delivery formats are among the most persistently misunderstood aspects of post-production. This guide covers the core facts — from the UHD/4K distinction through to cinema DCP specifications — without the ambiguity.
01 — Containers: HD, UHD, and the “4K” question
When someone says their television delivers “4K,” what they mean technically is UHD — Ultra High Definition. UHD is defined as a frame of 3,840 × 2,160 pixels. It is a consumer television standard established by the ITU, and it maintains the same 16:9 aspect ratio as standard HD. It is not cinema 4K.
HD (High Definition) is a 1,920 × 1,080 pixel container — also 16:9. UHD contains exactly four times the pixel count of HD: picture four HD frames arranged in a 2×2 grid and you have the UHD pixel grid. The image is sharper, but the shape of the frame is identical.
DCI 4K — true cinema 4K, defined by the Digital Cinema Initiatives — is a frame of 4,096 × 2,160 pixels. Note the horizontal difference: 4,096 versus 3,840. Cinema 4K is wider than UHD, with a native aspect ratio of approximately 1.90:1 rather than 1.78:1. The same body defines DCI 2K as 2,048 × 1,080 pixels — the same proportions scaled down.
A UHD television is not displaying cinema 4K. The pixel counts differ, the colour science differs, the container proportions differ. These are related but entirely distinct formats — and producers should not conflate them in delivery specifications.
02 — Aspect Ratios: what lives inside the container
A container is the pixel grid — the total frame dimensions. An aspect ratio is the shape of the image content delivered within that container. These are two distinct things, and confusing them is one of the most common delivery errors.
The most familiar ratio is 16:9, expressed as 1.78:1 in decimal form. It is the native shape of HD and UHD containers. When 16:9 content is delivered in a 16:9 container, there are no black bars — the image fills the frame completely.
Not all content is shot or mastered at 16:9. When a wider image is placed in a 16:9 container — for example, a 2.39:1 scope film in a UHD frame — the image is letterboxed: horizontal black bars appear at the top and bottom of the frame to pad the unused area. When a narrower image is placed in a 16:9 container — such as a 4:3 archive clip — it is pillarboxed: vertical black bars flank the image on the left and right.
Black bars are not a flaw. They are the mathematically correct consequence of placing content that has one aspect ratio inside a container with a different one. The picture information is intact — the bars simply fill the unused container area.
Common aspect ratios at a glance
Note: 2.39:1 is the correct SMPTE designation for modern anamorphic scope. You may also see it referred to as 2.40:1 or — historically — 2.35:1. The distinction matters for delivery: Blu-ray’s anamorphic scope spec is specifically 1920 × 800, which is 2.40:1— a case where the rounding is actually codified in the format standard. For any delivery, always confirm the destination’s exact specification rather than assuming 2.39:1 universally.
03 — Broadcast & Streaming Delivery
Broadcast and streaming delivery is almost universally container-based, with the 16:9 frame as the outer boundary. Content at different aspect ratios — whether a widescreen film or a vertical social cut — is placed within that container with appropriate black padding.
Common delivery formats
Frame rates: a note on 23.976 vs 24
True 24 frames per second (24.000 fps) is increasingly common in digital production and streaming. The long-standing standard of 23.976 fps — technically 24000/1001 — was a consequence of NTSC colour television’s 29.97 fps system and remains prevalent in broadcast workflows for compatibility. When in doubt, confirm your delivery specification explicitly: most streaming platforms accept both, but some broadcast deliveries are strict.
For Australian broadcast delivery, the primary standard is 25 fps PAL. For US network deliveries, confirm whether 29.97 or 23.976 is required. International co-productions should specify frame rate per territory.
Colour space and transfer function
HD broadcast typically requires Rec. 709 colour space with a standard gamma transfer function. UHD/HDR deliveries may require Rec. 2020 colour space paired with either PQ (ST 2084) or HLG transfer functions, depending on the platform.
Dolby Vision is a proprietary HDR format that warrants separate mention because it is now a mandatory delivery requirement on several major streaming platforms — including Netflix, Apple TV+, and Disney+. Technically it uses Rec. 2020 colour space and the PQ transfer function, but adds a layer of dynamic metadata (the Dolby Vision RPU) that allows per-scene or per-frame brightness and colour mapping at the display. This is distinct from HDR10, which carries static metadata only. A Dolby Vision delivery is typically structured as a dual-layer package: a base HDR10 layer (for non-Dolby displays) plus the Dolby Vision enhancement layer. Producing a Dolby Vision master requires a licensed Dolby Vision pipeline and is subject to platform-specific technical specifications — do not assume an HDR10 master can be upgraded to Dolby Vision without this additional step.
Colour science is a separate consideration from frame size — always confirm colour space, transfer function, and HDR format requirements alongside resolution specifications in your delivery requirements document.
04 — Cinema: DCP Delivery
Theatrical release in commercial cinemas requires delivery as a Digital Cinema Package (DCP) — a specific, standardised set of files defined by the Digital Cinema Initiatives (DCI). DCPs are not video files in the conventional sense: they are a collection of encrypted, compressed image and audio assets formatted specifically for digital cinema servers.
DCP delivery uses the DCI container formats described in Section 01: either a 2K container (2048 × 1080) or a 4K container (4096 × 2160). Within those containers, there are three recognised presentation formats, defined by the aspect ratio of the content image.
DCP Flat — 1.85:1
DCP Flat places a 1,998 × 1,080 pixel active image inside the 2K container (2,048 × 1,080). The image does not fill the full container width — there are 25 pixels of inactive area on each side of the frame. In the 4K container, the active image scales to 3,996 × 2,160 within the 4,096 × 2,160 container.
DCP Scope — 2.39:1
DCP Scope places a 2,048 × 858 pixel active image inside the 2K container (2,048 × 1,080). The image occupies the full width of the container, with 111 pixels of inactive letterbox area above and below the active frame — centred vertically within the container. In the 4K container, the active image scales to 4,096 × 1,716 within the 4,096 × 2,160 container, with 222 pixels of letterbox split equally top and bottom.
DCP Full Container — ≈ 1.90:1
A third option exists and is formally recognised: delivering at the full container resolution — 2,048 × 1,080 (2K) or 4,096 × 2,160 (4K) — with no inactive area. This produces a native container aspect ratio of approximately 1.90:1. It is a legitimate delivery path and is notably how IMAX DCPs are configured, taking advantage of the full DCI container width for maximum screen coverage. For standard theatrical delivery however, projection systems are calibrated around two hard macros — Flat and Scope — each with a fixed zoom, lens position, and screen masking. A full-container DCP sits between these presets and requires the projectionist to configure a custom presentation, which many commercial venues will not do without prior coordination. For boutique cinemas, film festivals, and IMAX deliveries, it is straightforward; for wide theatrical release, confirm with the exhibitor before committing to this approach.
A DCP is not a video file — it is a package. The standard includes JPEG 2000 encoded image sequences (MXF-wrapped), multi-channel audio (up to 16 channels), subtitles, and metadata. It may be encrypted with KDM (Key Delivery Message) keys tied to specific screens and exhibition dates. Producing a DCP from a finished master requires a dedicated encoding step and, for deliveries to major exhibitors, third-party verification.
Cinema frame rates
The DCI specification supports a range of frame rates, but the global theatrical standard remains 24 frames per second. High Frame Rate (HFR) presentations at 48 fps have been used for specific releases but require compatible projector configurations at the cinema and are not standard delivery. All DCP masters should be confirmed at 24.000 fps unless an HFR release has been explicitly contracted and confirmed with the exhibitor.
05 — Key Distinctions — Quick Reference
Delivering with confidence
Navigating delivery specs shouldn’t fall on a producer alone. At Xenon Post, we work through the technical requirements of every project with you — broadcast, streaming, or theatrical — so nothing reaches a mastering stage with unresolved specification questions.
Talk to the team