Game Development Reference
In-Depth Information
Fig. 9.3
Hierarchical Rate-GoP structure for Low Delay Case
Fig. 9.4
Hierarchical Rate-GoP structure for Random Access Case
in the Rate-GoP, which is usually called the key frame, and other frames in the same
Rate-GOP are referenced less with less importance than the key frame.
The coding performance can be improved by amplifying the Lagrangianmultiplier
of the key frame in under random access (RA) and low delay P (LDP) test conditions.
The simulation results show that 5.9% coding performance can be achieved under
LDP condition.
The Lagrangian multiplier is calculated according to the quantization parameter,
which can be represented as follows:
2
qp
/
4
ʻ
=
const
×
(9.17)
The Lagrangian multiplier is further adjusted according to the picture type, which is
shown as follows:
ʻ
=
ʻ
∗
const
1
(9.18)
The constant const1 is assigned to different values according to different common test
conditions, which const1 equals 0.8 under LDP test conditions, and const1 equals 0.8,
1.0 and 1.2 for I pictures, P pictures and B pictures, respectively. Through adjusting
the Lagrange factor, the pictures that are referenced by other pictures are coded with
more bitrates, and hence with better quality.
Moreover, the Lagrangian multiplier is adjusted according to the coding layer
of each picture. Generally, the picture is more important with lower coding layers
than with upper coding layers, as the lower coding pictures will be referenced by
the subsequent pictures. Hence the Lagrangian multiplier of the upper coding layers
is amplified to reduce bitrates, and the Lagrangian multiplier of lower layers is
