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.
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.).
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.
A Device is a logical block of functionality within a networked media infrastructure. Examples of Devices include:
- 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 is video, audio or other data.
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.
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.
A Node is a logical host for Devices. This can be physical, or virtual (and a Node can be within a “cluster” or “cloud”).
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.
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
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).