Game Development Reference
In-Depth Information
Table 9.5 Corresponding payload structure of type in PSI
Type
Payload structure
Full name of payload structure
0
Undefined
-
1C23
Single NALU
Single NALU packet
24
STAP-A
Single-time aggregation packet—A
25
STAP-B
Single-time aggregation packet—B
26
MTAP16
Multitime aggregation packet with 16-bit offset
27
MTAP24
Multitime aggregation packet with 24-bit offset
28
FU-A
Fragmentation unit—A
29
FU-B
Fragmentation unit—B
30-31
Undefined
-
But different from the payload type of a NALU specified in Table 9.4 , the type field
here indicates the payload structure as shown in Table 9.5 .
This payload format specifies three cases of packetization modes: single NALU
mode, noninterleaved mode, and interleaved mode. In the single NALU mode or
the noninterleaved mode, NALUs are transmitted in NALU decoding order. The
interleaved mode allows transmission of NALUs out of NALU decoding order. As
an example, an RTP packet containing an STAP-A and two single-time aggregation
units is shown in Fig. 9.8 .
The payload format parameters are specified in the format of multipurpose internet
mail extension (MIME) (Freed and Borenstein 1996 ) strings. The media type name is
“audio” or “video,” while media subtype name is specified as “AV31” or “AVS1-P2,”
respectively. These parameters and other optional media type parameters are mapped
to corresponding fields in session description protocol (SDP) (Handley et al. 2006 ).
Furthermore, an informative implementation guideline on de-packetization
process is provided. The de-packetization process is implementation dependent. All
normal RTP mechanisms related to buffer management apply. In particular, dupli-
cated or outdated RTP packets (as indicated by the RTP sequences number and the
RTP time-stamp) are removed. To determine the exact time for decoding, factors
such as a possible intentional delay to allow for proper interstream synchronization
should be factored in.
Fig. 9.8 An RTP packet
containing an STAP-A and
two single-time aggregation
units
 
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