3.1.5.33.2 User agent behavior of a=x-source attribute

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A user agent SHOULD<60> include an a=x-source attribute in an m=audio or m=video media description, if media from an attached media source device might be sent on the media stream. For example, if the media stream will be sending media from an audio input device or video camera, an a=x-source attribute can give a descriptive name for the media source, such as "main camera". The a=x-source attribute for an active media description SHOULD NOT be removed in a subsequent SDP offer or SDP answer, even if the media source device is currently paused.

The presence of the a=x-source attribute also indicates that status information about the media stream SHOULD be published to other participants within the conference.

An MCU user agent SHOULD NOT include the a=x-source attribute in its media descriptions.