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compression ratio (algorithm complexity) and the
compression efficiency (real time) between the trade-offs.
First, we can shield the most time-consuming some of the
features of H.264, such as B frames, the encoder with only
the I frames and P-frame coding, did not use B frames, SIframe,
SP frame. Entropy coding using only generalpurpose
variable-length coding (UVLC), and the codec in
its process, by adjusting the code table look-up table used
in the binary tree algorithm, etc., further reducing the
computational complexity. Second, can the motion
estimation, multiple reference frames and the adaptive
time-consuming sub-block size of the larger parts of the
algorithm optimization. In intra prediction, using the
neighboring blocks have been intra-coded coding mode,
some pixels of the Cost values and valve limits, a
reasonable choice of the forecasting models the current
block in advance out of the forecasting process[5].
In the inter-frame encoding mode selection in the use of
a rapid inter-frame encoding mode selection algorithm.
The search process in motion by adding rate-distortion
optimization system, a balanced consideration of the
quality of coding and computational complexity, the use
of processed blocks of the adjacent projections
information, a reasonable estimate of the current block is
most likely to use forecasts frame, block shape and
predicted position, time out of forecasting process. In the
integer search using the improved asymmetric crossshaped
multi-layered hexagonal search algorithm
(UMHexagonS), this algorithm is compared with the
original H.264 fast full-search algorithm used in the
calculation of the amount of the savings of more than 90%,
especially in the Large movements of high bit-rate image
sequence coding, while maintaining a good rate-distortion
performance under conditions of very low computational
complexity; in 1 / 2 pixel, 1 / 4 pixel search using fast
algorithm for fractional pixel motion estimation, greatly
reducing the the computational complexity and improve
the search accuracy.
In the deblocking filter, taking into account the final
results of video encoding and decoding receiver object is
the human eye, the human eye to color brightness
sensitivity is far greater than the sensitivity; and under the
principle of deblocking filter can be aware of , when the
intensity of the more hours, blocking the more obvious,
and therefore intensity of less than 3, not do chroma
filtering Although this would be detrimental to image
quality, but the experiments prove that damage is not
obvious, Deblocking Filter amount of computation is
reduced by 30% or so.
Audio processing module, including audio data
collection, encoding, decoding and playback. In this
system, using the Windows Multimedia Audio of the
wave function is set and ACM (Audio Compression
Manager) to achieve the audio data collection, coding and
decoding, playback using DirectX components of the
process is one of the DirectSound audio codec technology
adoption the G.723, G.711 and G.729 technology for the
user to choose.
B. Network TCP / IP Transmission Module
The system uses a distributed multipoint conferencing
mode, rather than using a centralized multipoint
conferencing mode. The main reason is that centralized
multipoint conferencing method must be used MCU.
While the MCU is often very expensive, not suitable for
ordinary users. Distributed Multipoint mode using
multicast technology, which can effectively reduce the
burden on the network to avoid unnecessary waste of
resources.
Network Transmission Systems transport layer is
divided into modules and systems network layer transport
layer protocols include TCP and UDP protocols both too,
UDP protocol Fortunately, real-time performance in the
LAN. However, in WAN. As the ever-changing network
environment, will inevitably produce delay, jitter and
other issues, it will seriously affect the amount of audio
and video effect.
To this end, the system in the above agreement on the
basis of the two plus the RTP / RTCP protocol. In order to
meet the real-time audio and video, audio and video
information is transmitted using UDP protocol; and apply
to enter the meeting, the President permission to get in and
out of meetings and other basic control information using
TCP protocol for reliable transmission; data reconciliation
packages this package modules to complete. System, the
transport layer from the Windows platform, complete the
WinSock specification, the system object by all of the
communication processes in the Microsoft c + + class
derived CAsyneSoeket made. These objects include a
video communication process, the audio communication
process, to receive quality information feedback
communication process, the meetings management
process and other communications in the network layer is
to comply with TCP / IP in the IGMP protocol, the system
uses the standard Windows Socket2.0-specific multicast
preparation of multicast communication module API.
The aforementioned system, several communication
process. Where are all based on UDP multicast
communication process.
C. Network Quality Control Module
Quality control module in the network to fully integrate
the H.264 codec features and audio codec features are
basically solved the video, audio, due to the phenomenon
of discontinuous bit stream structure of H.264 network
adaptability, using a "network-friendly" the structure and
syntax, and have error recovery capability, which would
facilitate the handling of error and packet loss, but also
makes the network quality control than H.263, MPEG-4
and other video conferencing systems better. First, by a
source within the RTP header description, serial number,
time stamp and other information, and the number of
RTCP provides contracting, contract time, the number of
received packets, received the same package networkrelated
information, to achieve the right to determine the
status of network transmission. In determining the
network conditions used in two ways[6]:
(1) compared the amount of data sent each other and
their own side to receive the amount of data to calculate
the loss rate, determine the network data transmission
situation;
(2) the packet round-trip time to judge.
Secondly, H.264 encoder based on network of
independently adjustable quantization step size to adapt to
channel coding. In the H 264 and also made use of data
partitioning method to deal with the channel bit rate
changes. Generated in the encoder has a different priority
of video data to support the network quality of service
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