Game Development Reference
In-Depth Information
base media file format (BMFF) (ISO/IEC
2005
) is exploited by extending specific
elementary streams and sample definitions, and a metadata track for timed metadata
to support surveillance applications. In addition, the common RTP payload format is
augmented by introducing a payload structure indication (PSI) byte as the first byte
of the RTP payload to identify different payload structures. In the following subsec-
tions, we give a detailed introduction of metadata organization in system layer by
taking the system standard of IEEE 1857 as an example.
9.2.1 File Format for IEEE 1857 Video and IEEE 1857.2
Audio
To provide a network-friendly environment for the transmission of video data, net-
work abstraction layer (NAL) unit is defined by AVC/H.264 (ISO/IEC
2009
). It
is a type of packetization of layer that prefixes certain headers to encoded video
bit stream. It mainly addresses the video-related applications such as video tele-
phony, video storage, broadcast and streaming applications, IPTV, etc. However, the
encoded bit stream from the source code standard-IEEE 1857 is a raw format bit-
stream. Therefore, Similar to AVC file format (ISO/IEC
2004
), we need to convert
the bitstreams of IEEE 1857 video and IEEE 1857.2 audio into NAL unit streams
and then store them into the file format.
9.2.1.1 NAL Mapping with Raw Format Bitstreams
The conversion process from IEEE 1857 video to NAL unit stream is as follows:
first, map the data between every two consecutive start code prefixes (0x000001) in
the video bitstream (including start code values but excluding start code prefixes)
into the NAL unit (NALU) data, and then insert an NALU header before the NALU
data according to the start code value and its context. The format of an NALU
header is shown in Fig.
9.7
is a forbidden zero bit while NRI is for NALU reference
identification and Type is for the NALU type (see Table
9.4
). In order to locate the
start of NALU, a 4-byte sequence of NALU de-limiter is added after every NALU
with value '0000 0000 0000 0000 0000 0000 0000 0001' or '0x000001'. A series of
NALUs that constitute a frame of coded picture forms an access unit. All data within
the same access unit should have the same time-stamp value for RTP packetization.
When the decoder receives the NAL unit stream, before decoding, it shall discard
each NALU header and the NALU de-limiters, and then insert a start code prefix
Fig. 9.7
Format of NALU
header
