RTMP Part 3 - Message Format

This part will describe about RTMP message format.

RTMP message is used for communication between client and server for any type of message. It contains a header and a payload

The message header contains

The payload can contain any information include video and audio data.

Protocol control message are messages that are required by RTMP and its chunk message. It has a message id of 1 to 7. ID 1 and 2 are for RTMP chunk message, ID 3 to 6 are for RTMP and ID 7 is for edge server and origin server

Protocol control message must have

1. Message stream id 0

2. Chunk stream id 2

3. Sent as highest priority

4. Fixed size payload

Below are the 7 types of message

Set Chunk Size (ID 1) is used to notify new chunk size to be used

Abort Message (ID 2) is used to notify receiver to discard any partially received message

Acknowledgement (ID 3) is used tell sender that the receiver is receiving bytes equal to the window size. Window size is the maximum number of bytes received without any acknowledgement message

User Control Message (ID 4) is used to notify peers with user control event

The following user control event type are supported

Window Acknowledgement Size (ID 5) is used to inform peers the window size to use when sending acknowledgement

Set Peer Bandwidth (ID 6) is used to inform output bandwidth for the peers

Reference: Adobe Official RTMP Specification