FU-A && STAP-A

RTP Payload Format for H.264 Video

NAL Unit Header

      +---------------+
      |0|1|2|3|4|5|6|7|
      +-+-+-+-+-+-+-+-+
      |F|NRI|  Type   |
      +---------------+

      Table 1.  Summary of NAL unit types and the corresponding packet
                types

      NAL Unit  Packet    Packet Type Name               Section
      Type      Type
      -------------------------------------------------------------
      0        reserved                                     -
      1-23     NAL unit  Single NAL unit packet             5.6
      24       STAP-A    Single-time aggregation packet     5.7.1
      25       STAP-B    Single-time aggregation packet     5.7.1
      26       MTAP16    Multi-time aggregation packet      5.7.2
      27       MTAP24    Multi-time aggregation packet      5.7.2
      28       FU-A      Fragmentation unit                 5.8
      29       FU-B      Fragmentation unit                 5.8
      30-31    reserved                                     -

STAP-A(聚合包)

     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                          RTP Header                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |STAP-A NAL HDR |         NALU 1 Size           | NALU 1 HDR    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         NALU 1 Data                           |
    :                                                               :
    +               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |               | NALU 2 Size                   | NALU 2 HDR    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         NALU 2 Data                           |
    :                                                               :
    |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                               :...OPTIONAL RTP padding        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Figure 7.  An example of an RTP packet including an STAP-A
               containing two single-time aggregation units

其中STAP-A NAL HDR格式如下

      +---------------+
      |0|1|2|3|4|5|6|7|
      +-+-+-+-+-+-+-+-+
      |F|NRI|  Type   |
      +---------------+

F和NRI取NALU 1 HDR的F和NRI，Type = 24

FU

     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | FU indicator  |   FU header   |                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
    |                                                               |
    |                         FU payload                            |
    |                                                               |
    |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                               :...OPTIONAL RTP padding        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Figure 14.  RTP payload format for FU-A

     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | FU indicator  |   FU header   |               DON             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
    |                                                               |
    |                         FU payload                            |
    |                                                               |
    |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                               :...OPTIONAL RTP padding        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Figure 15.  RTP payload format for FU-B

The FU indicator octet has the following format:

       +---------------+
       |0|1|2|3|4|5|6|7|
       +-+-+-+-+-+-+-+-+
       |F|NRI|  Type   |
       +---------------+
Values equal to 28 and 29 in the type field of the FU indicator octet identify an FU-A and an FU-B, respectively. 
The use of the F bit is described in [Section 5.3].  
The value of the NRI field MUST be set  according to the value of the NRI field in the fragmented NAL unit.

The FU header has the following format:

      +---------------+
      |0|1|2|3|4|5|6|7|
      +-+-+-+-+-+-+-+-+
      |S|E|R|  Type   |
      +---------------+

   S:     1 bit
          When set to one, the Start bit indicates the start of a
          fragmented NAL unit.  When the following FU payload is not the
          start of a fragmented NAL unit payload, the Start bit is set
          to zero.
E:     1 bit
          When set to one, the End bit indicates the end of a fragmented
          NAL unit, i.e., the last byte of the payload is also the last
          byte of the fragmented NAL unit.  When the following FU
          payload is not the last fragment of a fragmented NAL unit, the
          End bit is set to zero.

   R:     1 bit
          The Reserved bit MUST be equal to 0 and MUST be ignored by the
          receiver.

   Type:  5 bits
          The NAL unit payload type was the fragmentation nalu type.