Page 85 - Video Coding for Mobile Communications Efficiency, Complexity, and Resilience

62 Chapter 3. Video Coding: Standards

In order to facilitate optimal usage in a number of environments, this mode
contains two submodes:

1. The Rectangular Slice (RS) submode: When RS is in use, the slice
occupies a rectangular region of width speci/ed in units of macroblocks
and contains a number of macroblocks in scanning order within the
rectangular region. When RS is not in use, the slice contains a number
of macroblocks in scanning order within the picture as a whole.
2. The Arbitrary Slice Ordering (ASO) submode: when ASO is in use,
the slices may appear in any order within the bitstream. When ASO is
not in use, the slices must be sent in scanning order.

A slice video picture segment starts at a macroblock boundary in the picture
and contains a number of macroblocks. Di1erent slices within the same picture
shall not overlap with each other, and every macroblock shall belong to one
and only one slice.
A slice is de/ned as a slice header followed by consecutive macroblocks
in scanning order. In order to allow slice header locations within the bitstream
to act as resynchronization points for bit error and packet loss recovery and
in order to allow out-of-order slice decoding within a picture, slice bound-
aries are treated di1erently than simple macroblock boundaries. Thus, no data
dependencies can cross the slice boundaries within the current picture. An
exception to this is the Deblocking Filter mode, which, when in use without
the Independent Segment Decoding mode, /lters across the boundaries of the
blocks in the picture.

3.4.6.6 Supplemental Enhancement Information Mode (Annex L)
In this mode, additional supplemental information can be included in the bit-
stream to signal an enhanced display capability or to provide information for
external usage. The supplemental information may be present in the bitstream
even though the decoder may not be capable of providing the enhanced capa-
bility to use it or even to properly interpret it. In this case, the decoder can
simply discard the supplemental information. The mode can be used to signal
the following capabilities:

1. Picture Freeze: The mode can be used to signal that the contents of the
entire prior-displayed picture, or a speci/ed rectangular part of it, shall
be kept unchanged. The mode can also be used to explicitly signal a
picture freeze release.

2. Picture Freeze with Resizing: The mode can be used to signal that the
contents of a speci/ed rectangular area of the prior-displayed picture