Networked Media Open Specifications

Explanation –Source

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Please ensure you have read the Summary and Definitions before considering the further detail covered by this page.

Understanding the Source Entity

The intention is that a Source (identified by a Source ID) provides an easy and convenient way to refer to a time-based signal or content in a manner that is agnostic to the means used to express it and the exact quality / accuracy of the expression. This use of the term Source should not be confused with the casual use of the word source to refer to multiple media signals relevant to an ‘outside source’ or similar (see the Appendix).

It is useful to appreciate that a Source represents what its member Flows have in common – that is, the time-based data that they all represent. The Source entity allows the content to be referred to without needing to refer to a specific Flow. In some scenarios it might be helpful to think of the Source as identifying the result of running a particular query on the ancestry relationships associated with a collection of Flows.

The Source entity has been defined so that a Source is practically useful and aids in interoperability. As a result, a Source ID can be:

A Source will sometimes be associated with a particular physical device but this is not necessarily the case. Consider the following two scenarios:

In each scenario the two Flows are expressions of a single Source – the physical device that produced each Flow is not relevant from a content processing perspective. It is already possible to identify the device that created a Flow using that device’s own identity (see AMWA IS-04).

It is important to understand that a Source cannot be used to describe arbitrary similarities between Flows: all Flows that are expressions of a Source must “appear the same” when rendered / decoded (other than differences in quality / accuracy). Additional Flows that are similar but do not meet this constraint will need to be associated with a different Source; other mechanisms will then be needed to describe the similarity between these Sources.

Guidance on how Sources can be applied to the handling of video and audio can be found in 3.0. Practical Guidance for Media

Notes on the Formal Definition of Source

Commentary on How Source is Defined

Broader definitions of Source were considered (that is, definitions that would permit more Flows to be members) but these were found to be problematic when analysing against the intended purpose of a Source.

For example:

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