Chapter 10

Glossary

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Looking for a term? Related terms are grouped under alphabetical headings, with links back to the chapters that explain them.

Some words, such as “stream,” mean different things depending on whether we’re talking about media or transport. The definitions below follow how we use them in this book.

Authentication and authorization

Authentication: establishing which identity an endpoint or user has.

Authorization: deciding what that identity may do, such as publishing a lecture or subscribing to it.

End-to-end encryption: content protection whose keys are held by the intended content endpoints, so an intermediate relay cannot read the protected payload. Routing metadata can remain visible.

Broadcast and catalog

Broadcast: moq.dev’s name for a collection of tracks in one publication, such as the lecture’s audio and video.

Catalog: media metadata describing the available tracks or renditions and how to decode them. The format and schema depend on the media layer in use.

Codec, container, and timestamp

Codec: a method for encoding and decoding media. The codec compresses pictures or sound; the transport delivers the resulting bytes.

Container: a framing format that packages encoded media with information needed to interpret it, such as timestamps. It is distinct from the codec.

Timestamp: a position on a media timeline. It is not automatically a wall-clock time or a measurement of network delay.

Connection and session

Connection: the transport carrying data between two endpoints. In our lecture, the publisher connects to the relay, and the viewer has another connection to that relay.

Session: the MoQ exchange running over that transport. The endpoints agree on a protocol version and settings so they can send requests and content.

IP, TCP, UDP, and QUIC

IP: the Internet Protocol, which addresses packets and supports forwarding between networks.

TCP: a transport providing a reliable, ordered byte stream in each direction of a connection.

UDP: a transport carrying separate datagrams without built-in retransmission or ordering.

QUIC: a secure transport over UDP with multiple ordered byte streams and connection-level congestion control.

Packet: a network transmission unit. Packet boundaries do not define MoQ object boundaries.

ACK: an acknowledgment telling the sender which transport data arrived. The player handles decoding and playback separately.

RTT: round-trip time, a measure of network delay to a peer and back.

Read the networking introduction and comparison tables.

Keyframe and rendition

Keyframe: in this guide’s simplified video examples, a picture providing a fresh decoding starting point. Exact random-access behavior depends on the codec and packaging.

Rendition: another encoding of the same content, such as a lower-resolution video. Switching renditions may require new decoder configuration and a new starting picture.

Latency, jitter, and congestion

Latency: delay between specified events. Always ask which events: packet send and receipt, capture and display, or another pair.

Jitter: variation in delay. A playback buffer can absorb some variation at the cost of additional latency.

Congestion: a condition where demand exceeds available network capacity, causing queues or loss. Application queues can also grow when production outpaces delivery.

MOQT, moq-lite, and hang

MOQT: Media over QUIC Transport, the IETF publish/subscribe protocol described by a versioned draft in this edition.

moq-lite: the smaller protocol model used by the moq.dev project, with implementation-specific compatibility support.

hang: the moq.dev media layer providing catalog and container conventions above its generic transport model.

Object, group, and subgroup

Object: an addressed unit in MOQT, identified by its full track name, group ID, and object ID within a scope. Normal objects carry application payloads; subscription delivery also uses payload-free end markers. An object is not necessarily a video frame.

Group: a collection of objects within a track. A media format can arrange groups as independent join points; the group boundary alone does not guarantee that the contained media can be decoded.

Subgroup: a delivery grouping of objects within one group, sent in ascending object-ID order on its subgroup stream. Stream-based subscription delivery carries a subgroup on a subgroup stream; FETCH uses its own stream representation. This is part of MOQT’s model and is omitted from moq-lite’s simpler model.

Read more in Tracks, Groups, and Objects.

Publisher, subscriber, and relay

Publisher: an endpoint that supplies requested objects. An original publisher first introduces the content.

Subscriber: an endpoint requesting and receiving a track.

Relay: an intermediary acting as subscriber upstream and publisher downstream. It forwards content and may cache objects.

Stream and datagram

Stream: here, usually a reliable ordered QUIC or WebTransport byte stream. A “live stream” in everyday speech is a different concept.

Datagram: an independently delivered message without QUIC retransmission on loss. It does not promise arrival or order and has a size limit.

Track and namespace

Track: the named sequence of groups a subscriber can request. Audio and each video rendition can use separate tracks.

Namespace: a tuple of byte sequences that, together with a track name, identifies a track. Slashes in this book make example components readable; they are not the wire encoding.

Scope: the set of servers within which a full track name identifies the same track.

Read more in Publishing and Subscribing.