RTCP

Overview

The RTCP protocol is used to exchange control messages between sender and receiver. Sender and receiver exchange the controlPort with a SETUP RTSP request and reply.

The RTPC header is 8 bytes long. The message types are made by Apple and don't appear in the RFC 3550 specifications.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      ---------------------------------------------------------------
0x0  | V |P|M|   -   |       PT      |            Length             |
     |---------------------------------------------------------------|
0x4  :                                                               :

Version (V) is 2 and padding (P) is 0. Bit 3 is used as marker (M) and set to 1 every time a new track is played. The length reports the overall packet size.

Time request - C→S

Type 211 only NTP

Time reply - S→C

type 212 only NTP

Retransmit request - C→S

type 213

Retransmit reply - S→C

type 214

Time announce - S→C

Time announce messages are type 215.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      ---------------------------------------------------------------
0x0  |         RTP Time Remote       |            Net ...            |
     |---------------------------------------------------------------|
0x4  |             ...Net            |           RTP Time            |
     |---------------------------------------------------------------|
0x8  |                           Time base (?)                       |
      ---------------------------------------------------------------

The Net field is an 8 bytes integer.