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13.2 Example of Multi-Picture Slice Interleaving

13.2. Example of Multi-Picture Slice Interleaving​

An example of multi-picture slice interleaving follows. A subset of a coded video sequence is depicted below in output order. R denotes a reference picture, N denotes a non-reference picture, and the number indicates a relative output time.

   ... R1 N2 R3 N4 R5 ...

The decoding order of these pictures from left to right is as follows:

   ... R1 R3 N2 R5 N4 ...

The NAL units of pictures R1, R3, N2, R5, and N4 are marked with a DON equal to 1, 2, 3, 4, and 5, respectively.

Each reference picture consists of three slice groups that are scattered as follows (a number denotes the slice group number for each macroblock in a Quarter Common Intermediate Format (QCIF) frame):

   0 1 2 0 1 2 0 1 2 0 1
   2 0 1 2 0 1 2 0 1 2 0
   1 2 0 1 2 0 1 2 0 1 2
   0 1 2 0 1 2 0 1 2 0 1
   2 0 1 2 0 1 2 0 1 2 0
   1 2 0 1 2 0 1 2 0 1 2
   0 1 2 0 1 2 0 1 2 0 1
   2 0 1 2 0 1 2 0 1 2 0
   1 2 0 1 2 0 1 2 0 1 2

For the sake of simplicity, we assume that all the macroblocks of a slice group are included in one slice. Three MTAPs are constructed from three consecutive reference pictures so that each MTAP contains three aggregation units, each of which contains all the macroblocks from one slice group. The first MTAP contains slice group 0 of picture R1, slice group 1 of picture R3, and slice group 2 of picture R5. The second MTAP contains slice group 1 of picture R1, slice group 2 of picture R3, and slice group 0 of picture R5. The third MTAP contains slice group 2 of picture R1, slice group 0 of picture R3, and slice group 1 of picture R5. Each non-reference picture is encapsulated into an STAP-B.

Consequently, the transmission order of NAL units is the following:

   R1, slice group 0, DON 1, carried in MTAP,RTP SN: N
   R3, slice group 1, DON 2, carried in MTAP,RTP SN: N
   R5, slice group 2, DON 4, carried in MTAP,RTP SN: N
   R1, slice group 1, DON 1, carried in MTAP,RTP SN: N+1
   R3, slice group 2, DON 2, carried in MTAP,RTP SN: N+1
   R5, slice group 0, DON 4, carried in MTAP,RTP SN: N+1
   R1, slice group 2, DON 1, carried in MTAP,RTP SN: N+2
   R3, slice group 1, DON 2, carried in MTAP,RTP SN: N+2
   R5, slice group 0, DON 4, carried in MTAP,RTP SN: N+2
   N2, DON 3, carried in STAP-B, RTP SN: N+3
   N4, DON 5, carried in STAP-B, RTP SN: N+4

The receiver is able to organize the NAL units back in decoding order based on the value of DON associated with each NAL unit.

If one of the MTAPs is lost, the spatially adjacent and temporally co-located macroblocks are received and can be used to conceal the loss efficiently. If one of the STAPs is lost, the effect of the loss does not propagate temporally.

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