Kamaelia.Protocol.SDP

Session Description Protocol (SDP) Support

The SDPParser component parses Session Description Protocol (see RFC 4566) data sent to it as individual lines of text (not multiline strings) and outputs a dictionary containing the parsed session description.

Example Usage

Fetch SDP data from a URL, parse it, and display the output:

Pipeline( OneShot("http://www.mysite.com/sessiondescription.sdp"),
          SimpleHTTPClient(),
          chunks_to_lines(),
          SDPParser(),
          ConsoleEchoer(),
        ).run()

If the session description at the URL provided is this:

v=0
o=jdoe 2890844526 2890842807 IN IP4 10.47.16.5
s=SDP Seminar
i=A Seminar on the session description protocol
u=http://www.example.com/seminars/sdp.pdf
e=j.doe@example.com (Jane Doe)
c=IN IP4 224.2.17.12/127
t=2873397496 2873404696
a=recvonly
m=audio 49170 RTP/AVP 0
m=video 51372 RTP/AVP 99
a=rtpmap:99 h263-1998/90000

Then parsing will return this dictionary:

{ 'protocol_version': 0,
  'origin'     : ('jdoe', 2890844526, 2890842807, 'IN', 'IP4', '10.47.16.5'),
  'sessionname': 'SDP Seminar',
  'information': 'A Seminar on the session description protocol',
  'connection' : ('IN', 'IP4', '224.2.17.12', '127', 1),
  'time'       : [(2873397496L, 2873404696L, [])],
  'URI'        : 'http://www.example.com/seminars/sdp.pdf',
  'email'      : 'j.doe@example.com (Jane Doe)',
  'attribute'  : ['recvonly'],
  'media':
      [ { 'media'     : ('audio', 49170, 1, 'RTP/AVP', '0'),
          'connection': ('IN', 'IP4', '224.2.17.12', '127', 1)
        },
        { 'media'     : ('video', 51372, 1, 'RTP/AVP', '99'),
          'connection': ('IN', 'IP4', '224.2.17.12', '127', 1),
          'attribute' : ['rtpmap:99 h263-1998/90000']
        }
      ],
}

Behaviour

Send individual lines as strings to SDPParser's "inbox" inbox. SDPParser cannot handle multiple lines in the same string.

When SDPParser receives a producerFinished() message on its "control" inbox, or if it encounter another "v=" line then it knows it has reached the end of the SDP data and will output the parsed data as a dictionary to its "outbox" outbox.

The SDP format does not contain any kind of marker to signify the end of a session description - so SDPParser only deduces this by being told that the producer/data source has finished, or if it encounters a "v=" line indicating the start of another session description.

SDPParser can parse more than one session description, one after the other.

If the SDP data is malformed AssertionError, or other exceptions, may be raised. SDPParser does not rigorously test for exact compliance - it just complains if there are glaring problems, such as fields appearing in the wrong sections!

If a producerFinished or shutdownMicroprocess message is received on the "control" inbox then, once any pending data at the "inbox" inbox has been processed, this component will terminate. It will send the message on out of its "signal" outbox.

Only if the message is a producerFinished message will it output the session description is has been parsing. A shutdownMicroprocess message will not result in it being output.

Format of parsed output

The result of parsing SDP data is a dictionary mapping descriptive names of types to values:

Session Description