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According to RFC 6184 in

5.6. Single NAL Unit Packet :

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|F|NRI|  Type   |                                               |
+-+-+-+-+-+-+-+-+                                               |
|                                                               |
|               Bytes 2..n of a single NAL unit                 |
|                                                               |
|                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                               :...OPTIONAL RTP padding        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

How can I know what is the size of RTP padding? and What's the purpose of RTP padding?

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MicrosoctCprog
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1 Answers1

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It's assumed that you know the packet size in advance, e.g. from the underlying protocol layer: UDP, TCP, SCTP and so on. So, if padding (P) bit is set to 1, you should read the last byte of the packet which contains a count of how many padding octets should be ignored, including the last byte itself.

The purpose of padding is clearly explained in Section 5.1 of RFC 3550:

Padding may be needed by some encryption algorithms with fixed block sizes or for carrying several RTP packets in a lower-layer protocol data unit.

user2610053
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