Glossary

Streaming terms, in plain English.

37terms you'll meet when building live video, from ingest protocols to the player. Short definitions, no jargon chains.

ABR (adaptive bitrate): Streaming the same video at several quality levels and letting the player switch between them as the viewer's network speeds up or slows down.; ABR ladder Segment
ABR ladder: The set of renditions (resolution and bitrate pairs) a video is encoded into for adaptive streaming, for example 1080p at 6 Mbps down to 360p at 0.8 Mbps.; ABR (adaptive bitrate)Rendition
AV1: A royalty-free video codec from the Alliance for Open Media. It compresses better than H.264 and HEVC but takes more computing power to encode.; Codec HEVC (H.265)

Backpressure: A way for a slow consumer to make a fast producer wait instead of dropping or endlessly buffering messages. TCP flow control is the classic example.
Bitrate: How much data per second a stream uses, usually in kilobits or megabits per second. Higher bitrate generally means better quality and more bandwidth.

CDN (content delivery network): A network of edge servers that caches video close to viewers, so playback starts faster and the origin isn't overloaded.; Edge Origin
CMAF: Common Media Application Format: one set of fragmented MP4 segments that both HLS and DASH can play, which cuts storage and enables low-latency chunked delivery.; HLS MPEG-DASH
Codec: The algorithm that compresses and decompresses video or audio, such as H.264, HEVC or AV1 for video and AAC or Opus for audio.
Content moderation: Detecting and acting on unwanted content, such as profanity, unsafe images or copyrighted material. Live moderation does it in the stream before viewers see it.

DRM: Digital rights management: encrypting video so only authorised players with a licence key can play it. Common systems are Widevine, FairPlay and PlayReady.

Edge: A CDN server near the viewer that serves cached video segments.; CDN (content delivery network)

Glass-to-glass latency: The total delay from the camera lens capturing a moment to that moment appearing on the viewer's screen.
GOP (group of pictures): The run of frames between two keyframes. Shorter GOPs let players join and switch quality faster but cost more bitrate.; Keyframe

H.264 (AVC): The most widely supported video codec. Almost every device can decode it, which makes it the safe default.; Codec
HEVC (H.265): The successor to H.264, with roughly half the bitrate for similar quality, but with patchier browser support and licensing costs.; Codec AV1
HLS: HTTP Live Streaming: Apple's protocol that splits video into small segments listed in a playlist, served over ordinary HTTP and CDNs.; LL-HLS Manifest
Hot spot: A partition or server that gets far more than its share of traffic, often because of how keys were split or one very popular item.; Partitioning (sharding)

Ingest: The first step of a live pipeline: receiving the video signal from a camera or encoder, usually over RTMP, SRT or WebRTC.

Jitter: Variation in how long packets take to arrive. Players and protocols use buffers to smooth it out.

Keyframe: A complete frame that can be decoded on its own. Other frames only store changes, so players need a keyframe to start or switch streams.; GOP (group of pictures)

LL-HLS: Low-Latency HLS: a version of HLS that delivers partial segments as they're made, bringing delay down to a few seconds while still using CDNs.; HLS

Manifest: The playlist file (.m3u8 for HLS, .mpd for DASH) that tells the player which renditions and segments exist.
MPEG-DASH: An open, codec-agnostic alternative to HLS that also streams segmented video over HTTP.; HLS CMAF

Origin: The server that holds the master copy of the stream's segments; CDN edges fetch from it.; CDN (content delivery network)

Packaging: Wrapping encoded video into delivery formats such as HLS or DASH, with manifests, segments and optional encryption.
Partitioning (sharding): Splitting a large dataset across several machines so each holds and serves a slice.; Hot spot

Rendition: One version of a video at a specific resolution and bitrate within an ABR ladder.; ABR ladder
RTMP: Real-Time Messaging Protocol: an older protocol still widely used to send live video from encoders to platforms such as YouTube and Twitch.

Segment: A short chunk of video, usually 2 to 6 seconds, that HTTP streaming players download one after another. Players switch quality at segment boundaries.
SFU (selective forwarding unit): A WebRTC server that receives each participant's stream and forwards it to others without re-encoding, which is how group calls scale.; WebRTC
Snapshot isolation: Giving each database transaction a consistent frozen view of the data as of its start. It prevents many anomalies but not write skew.; Write skew
SRT: Secure Reliable Transport: an open protocol for sending live video over unreliable networks, recovering lost packets with retransmission (ARQ).; Ingest
SSAI (server-side ad insertion): Stitching ads into the stream on the server so they play seamlessly and are harder to block.

Transcoding: Decoding a video and re-encoding it, usually into several renditions for adaptive streaming.

WebRTC: A browser standard for real-time audio and video, with delay well under a second. Used for calls, interactive streams and low-latency playback.; WHIP / WHEP SFU (selective forwarding unit)
WHIP / WHEP: WebRTC-HTTP Ingestion and Egress Protocols: simple HTTP standards for publishing (WHIP) and playing (WHEP) WebRTC streams.; WebRTC
Write skew: A concurrency bug where two transactions read the same data, each makes a safe-looking change to a different row, and together they break a rule.; Snapshot isolation

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