3.1.5.18.4 a=mid attribute
The a=mid attribute is used as an identifier of the media described by the m= line. This attribute SHOULD<30> be included.
Every time a new m= line media is added to the SDP message, the value of a=mid is incremented by 1.
The media-identifier-attribute has the following format in ABNF notation, as described in [RFC5234]:
-
media-identifier-attribute="a=mid:" 1*DIGIT CRLF