Kamaelia.Protocol.RTP.RTP

• component RTPDeframer
• component RTPFramer

• RTP Packet Framing and Deframing
  • Example Usage
  • RTPFramer behaviour
  • RTPDeframer Behaviour

RTP Packet Framing and Deframing

Send a dict specifying what needs to go into the RTP packet and RTPFramer will output it as a RTP frame.

RTPDeframer parses an RTP packet in binary string format and outputs a (seqnum, packet) tuple containing a sequence number and a dict structure containing the payload and metadata of the RTP packet. The format is the same as that used by RTPFramer.

These components simply format the data into the RTP packet format or take it back out again. They do not understand the specifics of each payload type. You must determine for yourself the correct values for each field (eg. payload type, timestamps, CSRCS, etc).

See RFC 3550 and RFC 3551 for information on the RTP speecification and the meaning and formats of fields in RTP packets.

Example Usage

Read MPEG Transport Stream packets (188 bytes each) from a file in groups of 7 at a time (to fill an RTP packet) and send them in RTP packets over multicast to 224.168.2.9 on port 1600:

class PrePackage(Axon.Component.component):
    def main(self):
        SSRCID = random.randint(0,(2**32) - 1)      # random unique ID for this source
        while 1:
            while self.dataReady("inbox"):
                recvData = self.recv("inbox")
                self.send(
                  { 'payloadtype' : 33,             # type 33 for MPEG 2 TS
                    'payload'     : recvData,
                    'timestamp'   : time.time() * 90000,
                    'ssrc'        : SSRCID,
                  },
                  "outbox")
            yield 1


Pipeline( RateControlledFileReader("transportstream",chunksize=7*188),
          PrePackage(),
          RTPFramer(),
          Multicast_Transceiver(("0.0.0.0", 0, "224.168.2.9", 1600)

Timestamps for MPEG TS in RTP are integers at 90KHz resolution (hence the x90000 scaling factor). A random value is chosen for the unique source identifier (ssrc).

Save the payload from a stream of RTP packets being received from multicast address 224.168.2.9 on port 1600 down to a file:

Pipeline( Multicast_transceiver("0.0.0.0", 1600, "224.168.2.9", 0),
          SimpleDetupler(1),                      # discard the source address
          RTPDeframer(),
          RecoverOrder(bufsize=64, modulo=65536), # reorder packets
          SimpleDetupler(1),                      # discard the sequence number
          SimpleDetupler("payload"),
          SimpleFileWriter("received_stream"),
        )

RTPFramer behaviour

Send to RTPFramer's "inbox" inbox a dictionary. It must contain these fields:

{
    'payloadtype' : integer payload type
    'payload'     : binary string containing the payload
    'timestamp'   : integer timestamp (32 bit, unsigned)
    'ssrc'        : sync source identifier (32 bit, unsigned)

...and these fields are optional:

    'csrcs'        : list of contributing source identifiers (default = [])
    'bytespadding' : number of bytes of padding to be added to the payload (default=0)
    'extension'    : binary string of any extension data (default = "")
    'marker'       : True to set the marker bit, otherwise False (default=False)
}

RTPFramer automatically adds a randomised offset to the timestamp, and generates the RTP packet sequence numbers, as required in the specification (RFC 3550).

RTPFramer constructs an RTP packet matching the fields specified and sends it as a binary string out of the "outbox" outbox.

If a producerFinished or shutdownMicroprocess message is received on the "control" inbox. It is immediately sent on out of the "signal" outbox and the component then immediately terminates.

RTPDeframer Behaviour

Send to RTPDeframer's "inbox" inbox a binary string of an RTP packet, and the packet will be parsed, resulting in a (seqnum, packet_contents) tuple being sent to the "outbox" outbox. It will have this structure:

( sequence_number,
  {
    'payloadtype'  : integer payload type
    'payload'      : binary string containing the payload
    'timestamp'    : integer timestamp (32 bit, unsigned)
    'ssrc'         : sync source identifier (32 bit, unsigned)
    'csrcs'        : list of contributing source identifiers, [] if empty
    'extension'    : binary string of any extension data, "" if none
    'marker'       : True if marker bit was set, otherwise False
  }
)

See RFC 3550 for an explanation of the precise purposes of these fields.

If a producerFinished or shutdownMicroprocess message is received on the "control" inbox. It is immediately sent on out of the "signal" outbox and the component then immediately terminates.

---

Kamaelia.Protocol.RTP.RTP.RTPDeframer

class RTPDeframer(Axon.Component.component)

RTPDeframer() -> new RTPDeframer component.

Deconstructs an RTP packet, outputting (seqnum, dict) tuple where seqnum is for recovering the order of packets, and dict contains the fields from the RTP packet.

Inboxes

Outboxes

Methods defined here

Warning!

You should be using the inbox/outbox interface, not these methods (except construction). This documentation is designed as a roadmap as to their functionalilty for maintainers and new component developers.

main(self)

parsePacket(self, packet)

shutdown(self)

Kamaelia.Protocol.RTP.RTP.RTPFramer

class RTPFramer(Axon.Component.component)

RTPFramer() -> new RTPFramer component.

Creates a complete RTP packet based on a dict structure describing the packet.

Inboxes

Outboxes

Methods defined here

Warning!

You should be using the inbox/outbox interface, not these methods (except construction). This documentation is designed as a roadmap as to their functionalilty for maintainers and new component developers.

constructPacket(self, content)

main(self)

shutdown(self)