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Extensions

The tt:Extension element adds information to the ONVIF scene description that isn't part of the standard object fields. Source UUIDs are one example of extension data. For a general description of UUIDs, see Universally unique identifier (UUID).

Source UUID​

The UUID attribute of a tt:Object identifies the resulting object. A tt:SourceUuid element identifies a source track that contributed to that object. An object can have several source UUIDs when data from multiple tracks or analytics sources has been combined.

The tt:Extension element stores source UUIDs in a tt:SourceUuids container. Each source UUID uses a separate tt:SourceUuid element:

<tt:Frame UtcTime="2026-09-02T10:15:30.000000Z">
    <tt:Object ObjectId="42" UUID="6ba7b810-9dad-11d1-80b4-00c04fd430c8">
        <tt:Extension>
            <tt:SourceUuids>
                <tt:SourceUuid>550e8400-e29b-41d4-a716-446655440000</tt:SourceUuid>
                <tt:SourceUuid>7c9e6679-7425-40de-944b-e07fc1f90ae7</tt:SourceUuid>
            </tt:SourceUuids>
        </tt:Extension>
    </tt:Object>
    <tt:Object ObjectId="43" UUID="6ba7b811-9dad-11d1-80b4-00c04fd430c8">
        <tt:Extension>
            <tt:SourceUuids>
                <tt:SourceUuid>f47ac10b-58cc-4372-a567-0e02b2c3d479</tt:SourceUuid>
            </tt:SourceUuids>
        </tt:Extension>
    </tt:Object>
</tt:Frame>

In this example, each UUID attribute identifies the resulting object. Object 42 has two tt:SourceUuid elements because two source tracks contributed to it. Object 43 has one source track.

Usage​

Source UUIDs let you correlate objects from different applications on the same device. One use case is matching Fusion Tracker objects with objects from AXIS Object Analytics (AOA).

To find a matching AOA object:

  1. Look for the Fusion Tracker object's UUID in the AOA scenarios.
  2. If no match is found, look for any of the object's source UUIDs in the AOA scenarios.