Reference

Glossary of TV, streaming and broadcast terms

44 terms defined in plain language — the vocabulary that turns up across streaming delivery, broadcast standards, video and audio formats, and the hardware in front of viewers.

Delivery

Adaptive bitrate streamingalso: ABR: A delivery method that encodes the same video at several quality levels and lets the player switch between them mid-playback as network conditions change. It is why a stream degrades to a softer picture instead of stopping outright.

Buffer: The stretch of video a player has downloaded but not yet shown. Playback stalls — 'buffering' — when the buffer empties faster than the network can refill it.

CDNalso: Content delivery network: A distributed network of servers that keeps copies of video segments close to viewers. It is the layer that decides whether a stream is served from a nearby city or from across an ocean.

DASHalso: MPEG-DASH: An adaptive streaming standard that describes available quality levels in an XML manifest. Functionally comparable to HLS and widely used alongside it.

DRMalso: Digital rights management: The encryption and licensing system that controls playback of protected content. DRM level is often what caps a device to standard definition on services that require hardware-backed protection for higher resolutions.

HLSalso: HTTP Live Streaming: Apple's adaptive streaming protocol, which splits video into short segments listed in a playlist file. It is the most widely deployed streaming format on the open internet.

Latency: The delay between something happening and a viewer seeing it. Conventional streaming runs tens of seconds behind broadcast, which is why streamed live sport can lag a neighbour's television.

Manifest: The index file a streaming player reads to learn which quality levels, audio tracks and subtitle tracks exist and where the segments are. Called a playlist in HLS and an MPD in DASH.

Transcoding: Converting already-encoded video into another format, resolution or bitrate — the step that produces the multiple quality levels adaptive streaming relies on.

Segment: One of the short files a stream is cut into, typically two to ten seconds long. Segments are what a player actually requests, and their length is a direct trade between live latency and compression efficiency.

Bitrate ladder: The set of quality levels a title is encoded into, from a low-resolution rung that survives a weak connection up to full quality. Adaptive streaming works by moving a player up and down this ladder during playback.

CMAFalso: Common Media Application Format: A container format that lets one set of media segments be referenced by both an HLS playlist and a DASH manifest, instead of storing two parallel copies. Its chunked form is the basis of most low-latency live streaming.

Low-latency streamingalso: LL-HLS, LL-DASH: Extensions to HLS and DASH that begin delivering a segment while it is still being written, rather than waiting for it to be complete. This cuts live delay to a few seconds while keeping the caching model that makes mass streaming affordable.

Unicast: Delivery in which each viewer receives their own individual stream. It is how streaming over the open internet works, and it is why cost and capacity rise with every additional viewer.

Multicast: Delivery in which one transmission is shared by many receivers, who join it rather than requesting a copy each. Used inside managed operator networks; broadcast is the over-the-air equivalent of the same idea.

IPTV: Television delivered using internet protocols. In its original technical sense it refers to services carried over an operator's own managed network, where quality can be controlled, as distinct from over-the-top delivery across the public internet. The term is now used more loosely.

Video on demandalso: VOD: Content that is delivered when a viewer chooses to start it, rather than at a scheduled time. The technical opposite of linear delivery, and unrelated to how the service is paid for.

Live streaming: Delivery of an event over IP while it is still happening. It uses the same machinery as on-demand streaming, with the added constraint that encoding, packaging and buffering all have to happen inside a time budget.

Video & audio

AV1: A royalty-free video codec developed by the Alliance for Open Media. It compresses more efficiently than H.264 and HEVC at the same quality, at the cost of heavier decoding, so hardware support determines which devices can play it smoothly.

Bitrate: The amount of data used per second of video or audio, usually in megabits per second. Higher bitrate generally means more detail retained, but the codec and encoding settings matter as much as the number.

Codec: The algorithm pair that compresses video or audio for transmission and decompresses it for playback. A device can only play what it can decode, which is why codec support is a hard compatibility limit rather than a preference.

Dolby Atmos: An object-based audio format that positions sounds in three-dimensional space rather than assigning them to fixed channels. What a viewer actually hears depends on the playback system's ability to render those objects.

Dolby Vision: An HDR format that carries scene-by-scene metadata so a display can adjust tone mapping frame by frame. It requires support in the content, the delivery chain and the display.

Frame rate: How many images are shown per second. Broadcast television has historically used 25, 30, 50 or 60 frames per second depending on region; film-sourced material is typically 24.

HDRalso: High dynamic range: A set of formats that widen the range between the darkest and brightest parts of an image and expand the colour range. HDR10, HDR10+, Dolby Vision and HLG are the common variants.

HEVCalso: H.265: A video codec roughly twice as efficient as H.264, and the codec ATSC 3.0 uses. Its licensing situation is a large part of why AV1 exists.

Resolution: The pixel dimensions of an image, such as 1920×1080 or 3840×2160. It sets an upper bound on detail but does not determine picture quality on its own — bitrate, codec and mastering usually matter more.

SDRalso: Standard dynamic range: The conventional brightness and colour range that television used before HDR, built around the limits of older display technology. Most archive material is SDR and is not improved by being shown on an HDR display.

Broadcast

ATSC 1.0: The digital terrestrial broadcast standard used in North America since the late 1990s. It carries MPEG-2 video over an 8-VSB signal and is what a conventional over-the-air tuner receives.

ATSC 3.0also: NextGen TV: The successor broadcast standard to ATSC 1.0, built on an IP transport. It supports HEVC video, higher resolutions, HDR, immersive audio, targeted data delivery and mobile reception — the ambition the earlier Mobile DTV effort could not carry.

DVB: The family of digital broadcast standards used across Europe and much of the world, covering terrestrial (DVB-T/T2), satellite (DVB-S/S2) and cable (DVB-C) transmission.

Mobile DTValso: ATSC-M/H: An extension to ATSC 1.0, standardised in 2009, that added a broadcast signal robust enough for moving receivers. Hardware shipped and services launched, but it never reached scale — its goals were folded into ATSC 3.0.

5G Broadcast: A transmission mode that sends television over high-power broadcast towers using 5G standards, receivable without a mobile subscription. It revisits the same problem Mobile DTV set out to solve, with newer tools.

MPEG transport streamalso: MPEG-TS: The container format used to carry broadcast television, designed to stay recoverable when part of the signal is lost. ATSC 1.0 and DVB are built on it; ATSC 3.0 replaces it with an IP transport.

EPGalso: Electronic programme guide: The schedule data a receiver displays as a grid of what is on now and next. On broadcast it is carried in the signal itself; streaming services generate the equivalent from their own metadata.

Devices & display

Local dimming: A backlight technique on LCD televisions that dims zones of the panel independently to deepen black levels. The number and control of zones determines how well it works.

OLED: A display technology in which each pixel emits its own light, so pixels can switch off completely. That produces true black and precise contrast without a backlight.

Set-top box: A separate device that receives and decodes television, whether from a broadcast tuner, a cable or satellite operator, or a streaming service, and outputs it to a display.

Upscaling: Reconstructing a higher-resolution image from a lower-resolution source. It cannot recover detail that was never captured, so its quality depends entirely on how well the processing estimates the missing information.

VRRalso: Variable refresh rate: A display feature that matches the screen's refresh rate to the incoming frame rate, removing judder and tearing. Mainly relevant to games, but it also affects how mixed-frame-rate video is presented.

Automatic content recognitionalso: ACR: A system built into many televisions that identifies what is on screen by fingerprinting the display output and matching it against a reference database. Because it works from the picture rather than from an app, it can identify content arriving from external devices.

Business models

FASTalso: Free ad-supported streaming television: Streaming channels that run on a linear schedule and are funded by advertising rather than subscription. Structurally they are broadcast television delivered over IP.

OTTalso: Over-the-top: Video delivered over the open internet rather than through a broadcaster's or operator's own managed network.

SVOD, AVOD and TVOD: The three common on-demand funding models: subscription, advertising, and transactional rental or purchase. Most large services now combine at least two.

Terms are added as coverage expands. If something you expected to find is missing, or a definition needs correcting, tell us.