Digital Signal Processing Reference
In-Depth Information
more efficiently than CAVLC but requires more processing power
to decode.
15.2.12 H.264 Redundant Slices
In lossy channels, redundant slices can be added, for all or part
of a frame. If there are no transmission errors, the decoder will
ignore the redundant slices. If a slice is corrupted, the decoder
can use the redundant slice instead. However, the addition of
redundant
slices
increases
the bit
rate and reduces
the
compression rate.
15.2.13 H.264 Arbitrary Slice Ordering
Slices are normally sequentially ordered from left to right and
from top to bottom. They are also transmitted in this order.
Arbitrary slice ordering (ASO) allows the slices to be transmitted
in any order. By transmitting out of order, and in some inter-
leaved fashion, the effect of errors can sometimes be reduced. In
a packetized system, the loss or corruption of a packet might
affect several slices. Normally, these would be adjacent slices, but
with ASO they can be spread out throughout the frame, mini-
mizing the visual impact of the packet error.
15.2.14 H.264 Flexible Macroblock Ordering
Extending the same idea as ASO, flexible macroblock ordering
can be used to further offset the effect of errors. Macroblocks are
normally coded sequentially in raster order within a slice.
However, it is possible to assign macroblocks to other slices,
thereby interleaving the macroblocks across the various slices of
a frame. There is a macroblock allocation map that describes
different options for distribution of macroblocks to the different
slice groups.
In the event of a corrupted slice, the macroblocks of that slice
are then in different regions of the frame, according to the mac-
roblock allocation map. Since the neighbors of the damaged
macroblock from the corrupted slice are intact, the damaged
macroblock can be concealed by interpolating from the intact
neighboring macroblocks.
15.2.15 H.264 Additional Features
There are many more features in various H.264 profiles, which
cannot be covered in any detail here. For example, numerous
features are provided to support streaming operation;
for
