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NMOS Glossary

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In NMOS, several common terms have specific meanings that it helps to be aware of. Many of these correspond to the glossary of the JT-NM Reference Architecture.

Several of these are formally defined in NMOS specifications, for example in the IS-04 Data Model, but are described here for convenience.

API

An Application Programming Interface provided over a protocol such as HTTP or WebSocket, defined in an AMWA NMOS Specification (IS-04, IS-05, IS-06, etc.).

Client

The entity that is using an API, for example:

  • a Node using the IS-04 Registration API
  • a monitoring application using the IS-04 Query API
  • a connection control application using the IS-05 Connection API

The Client is distinct from the User.

Controller

A Controller is Client software that interacts with the NMOS APIs to discover, connect and manage resources (Nodes, Devices, Senders and Receivers) within a networked media system.

Device

A Device is a logical block of functionality within a networked media infrastructure. Examples of Devices include:

  • Camera
  • SDI to IP adapter
  • Chroma keyer
  • Audio mixer

A Device can have a permanent presence on its Node (a fixed Device, e.g., a networked camera), or it can be created on demand by its Node (a virtual Device, e.g., a software-based transcoder). Nodes can dynamically create different types of Device (a dynamic Device).

Essence

Essence is video, audio or other data.

Flow

In the IS-04 and IS-05 specifications a Flow refers to a sequence of Essence Grains, that is video, audio or time-related data, generated by a Source. A Source can generate multiplexed Flows consisting of more than one kind of Essence.

This is a relatively high-level usage of the word, not to be confused with a low-level flow within the physical network (distinguished as a Network Flow in the IS-06 Data Model).

In addition to indicating the format of its Source, a Flow identifies the media type and parameters of the particular rendition.

Grain

NMOS uses Grain as a convenient way of identifying a unit of Essence, that is video, audio or time-related data. This helps with mapping NMOS's logical data model onto physical Specifications.

For example, a video Grain could correspond to a frame of video.

Node

A Node is a logical host for Devices. This can be physical, or virtual (and a Node can be within a "cluster" or "cloud").

In JT-NM TR-1001-1, the EBU Technology Pyramid, and other industry documents, the term Media Node is often used.

Receiver

A Receiver consumes a Flow transmitted on the network by a Sender.

A Receiver identifies the transport protocol it uses to communicate over the network and the data format it can accept.

Registry

A Registry, or Registration & Discovery Instance, is a Server that provides the IS-04 Registration API for Nodes and the IS-04 Query API for Controllers.

Sender

A Sender makes a Flow available on the network.

A Sender identifies the transport protocol it uses to communicate over the network.

For example, a Sender could transmit an RTP stream according to a payload mapping for a specific video format, or a sequence of data Grains via the MQTT or WebSocket protocols.

Server

The entity that is providing an API, for example:

  • a Registry implementing IS-04 Registration and Query APIs
  • a Node implementing IS-04 Node API and IS-05 Connection API

Source

A Source represents the logical origin of any number of Essence Flows, each of which is a rendition of the Source.

A Source therefore identifies the common format of its Flows.

For example, a Source could generate Essence based on its Device's input signals, such as a camera image sensor, HDMI input signal, received RTP streams, or an internally generated test pattern or file read from storage, etc.

Note that a Source is:

  • not a Device from which the content originates (for example there might be video, audio and perhaps data Sources associated with a camera, the camera itself is the Device not a Source).
  • not about the physical origin of the Flows (for example: two Flows associated with the same Source might physically originate from different hardware in distinct geographical locations).

User

Where specifications refer to a User, this can include both human operators who drive a Controller manually and automation systems that drive a Controller programmatically.