Game Development Reference
In-Depth Information
1. Video data NALUs (coded picture header, coded slice):
The picture header and all slice NALUs for a coded picture shall be contained
within the sample whose decoding time and composition time are those of the
picture. Each IEEE 1857 video sample shall contain at least one picture header
NALU and one slice NALU.
2. NALUs sequence:
The sequence of NALUs in an elementary stream and within a single sample shall
be in a valid decoding order for those NALUs as specified in IEEE 1857 video.
3. Timing information:
All timing information is provided by the information stored in the various sample
metadata tables. Timing provided within the IEEE 1857 video stream in this file
format should be ignored.
4. No start code prefixes:
The elementary streams shall not include start code prefixes. Systems that wish
to deliver, from this file format, a stream using start code prefixes will need to
reformat the stream back into IEEE 1857 video bitstream by inserting those start
code prefixes and discarding those NALU headers.
An IEEE 1857 video access unit is made up of one or a set of NALUs. Each
NALU is represented with the length of NALU and the NALU itself, where length
indicates the number of bytes of the following NALU.
9.2.2 RTP Format for IEEE 1857 Video and IEEE 1857.2
Audio
RTP is chosen for transmission of audiovisual content over IP network. Before using
RTP packetization rules, the audiovisual bitstream shall be converted to NAL unit
stream as introduced previously. Usage of the RTP header is almost the same as
defined in IETF RFC 3550 (Schulzrinne et al.
2003
). To be noted, the RTP time-
stamp is set as the sampling time-stamp of the content. In the case of video, a 90kHz
clock rate shall be used.
9.2.2.1 RTP Payload Format
Three basic payload structures are specified in IEEE 1857 system standard, namely,
Single NALU packet, Aggregation packet, and Fragmentation units (FUs). In a single
RTP payload, the Single NALU packet contains only one NALU while the Aggrega-
tion packet aggregates multiple NALUs. And the Fragmentation units will be used
to fragment a single NALU over multiple RTP packets. In order to make parsing the
payload structure easier, an additional byte is inserted as the first byte of the RTP
payload to identify different payload structures. This byte is called payload structure
indication (PSI), which has the same syntax as the NALU header shown in Fig.
9.7
.
