Page 94 - Video Coding for Mobile Communications Efficiency, Complexity, and Resilience

Section 3.4. The H.263 Standard 71

vectors. Instead, a new prediction method is used to allow independent motion
vector decoding in both the forward and backward directions.

3.4.7.3 Additional Supplemental Enhancement Information (Annex W)

This annex describes additional supplemental enhancement information that
adds to the functionality of the supplemental enhancement information mode
(annex L) of H.263+. In particular, the following additional information can
be added to the bitstream:
1. Indication of the use of a speci/c /xed-point IDCT.

2. Picture messages, including the message types of:
(a) Arbitrary binary data.

(b) Text (arbitrary, copyright, caption, video description, or uniform
resource identi/er).

(c) Picture header repetition (current, previous, next with reliable tem-
poral reference, or next with unreliable temporal reference).

(d) Interlaced /eld indications (top or bottom).
(e) Picture number.
(f ) Spare reference picture identi/cation.

3.4.7.4 Pro>les and Levels De>nitions (Annex X)
With the variety of optional modes available in H.263, it is crucial that sev-
eral preferred mode combinations for operation be de/ned so that di1erent
terminals will have a high probability of connecting to each other. This an-
nex contains a list of preferred mode combinations, which are structured into
“pro/les” of support. It also de/nes some groupings of maximum performance
parameters as “levels” of support for these pro/les.
The annex de/nes nine pro/les (pro/le 0 to pro/le 8). Each pro/le is
de/ned in terms of a set of features supported by the decoder. For example,
the Baseline Pro4le (pro/le 0) refers to the syntax of H.263 with no optional
modes of operation. Another example is Version 2 Interactive and Streaming
Wireless Pro4le (pro/le 3). This pro/le is de/ned to provide enhanced coding
e,ciency performance and enhanced error resilience for delivery to wireless
devices within the feature set available in H.263+. This pro/le of support is
composed of the baseline design plus the following modes: advanced INTRA
coding mode (Annex I), deblocking /lter mode (Annex J), slice structured
mode (Annex K), and the modi/ed quantization mode (Annex T).