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QoS, each frame data is divided into several parts
according to their importance in the network congestion,
buffer overflow will be discarded less important
information; encoder will be the status of the network
independently of the frame for some important noncoding,
non-transmission.
Taking into account the sensitivity of people to the
sound signal is higher than the video signals and audio
signals in the video conference is more important than the
video signal. When the two data streams to compete on
the same network resources, give priority to the amount of
audio data in order to reduce the pressure on the network,
in the audio encoder detected an increase of silence, only
speaking participants to send the audio data; in order to
ensure the continuity of audio data, In the audio decoder
side opened a larger buffer, when the data received
enough for a long time. Through the data packet to
determine whether the timestamp on the data for the same
time, evenly played.
D. Conference Management Module
Conference management support throughout the
meeting process, not only to manage and coordinate all
the resources used in meetings, including the transmission
path, communication protocols, codecs, media access,
display and related information, but also manage the
meeting process, including initiation, maintenance, from
the will and voice control. Conference Manager has six
components: membership information database, the
registered membership, speaking handling, process
management, information query, from the Club
Management. The management of the entire conference
by the President ended the meeting manager and members
of the coordination of client meetings manager to resolve.
This system allows the Conference Manager can be
dynamically expanded scale of the meeting, members are
free to join, from the council[7].
III. SYSTEM TESTING
As a result of this system is the full software program,
simply P4 level of PC machines can be achieved, which
will greatly reduce the user's costs for the general ordinary
users. H.264 codec software through the machine to
complete. As the complexity of H.264 is the H.263 coding
ten times. Coding is the key to the whole system, of which
the video encoding rate, encoding rate and decoding speed
determines the overall system performance[8].
Desktop video conferencing systems throughout the test
platform is P4/2.4GHz 512M RAM of the PC machines
and Win2000 professional system, test software is used in
the official test H.264 source code, by the German
Institute for hhi responsible for the development of the
JM8.6[3] generated by VC7.1 compile release version,
JM8.6 using basic subset (baseline profile). In the
parameter setting off some of the H.264 encoding
performance, the contribution of the small but very high
degree of computational complexity of the new features,
such as multiple reference frames, unnecessary inter
prediction block mode, CABAC and so on.
When the video resolution of 176x144, frame rate of 15
frames per second, audio to G.723 (5.3 k) mode
conditions, all the way video takes about close to 150kHz
bandwidth. Way audio to account for less than 6kHz
bandwidth, the bandwidth occupied primarily video.
System supports a maximum resolution of images is
352X288, video frame rate of 30fps, the maximum rate of
2Mbps.
Test
Sequence
TABLE I.
IPERFORMANCE OF VIDEO ENCODING SYSTEM
Coding
time
PSNR
(y)
PSNR
(u)
PSNR
(v)
foreman 4.446S 29.86dB 37.37dB 37.94dB
Mother_D 3.238S 35.32dB 39.86dB 40.12dB
Actual
Rate
64.3
Kbps
64.2
Kbps
Table l lists the PC to complete the video encoding with
pure efficiency. All the sequence 150, target rate of
64Kbps. The source frame rate to 15fps, target frame rate
of l5fps.
In JM8.6 default parameters, using the basic subset
(baseline profile) and use the same test sequence.
Measured performance data listed in Table 2.
TABLE II.
H.264 VIDEO CODING PERFORMANCE(JM8.6 BASELINE PROFILE)
Test
Sequence
Coding
time
PSNR
(y)
PSNR
(u)
PSNR
(v)
Foreman 347.81S 35.79dB 39.14dB 40.51dB
Mother_D 311.63S 37.37dB 41.58dB 41.93dB
IV.
ANALYSIS
Actual
Rate
134.53
Kbps
126.28
Kbps
Data Analysis: From the comparison of before and after
optimization, we can see that the PSNR drop 1-5dB
circumstances, the subjective image decline in the quality
is not significant. But comparing the before and after the
encoding rate, is indeed a huge increase, and this in the
video conferencing system to improve the system for realtime
is very critical[9].
(1)a software-based H.264 video conferencing system
uses the H.264 standard, can be achieved at low bit rates
higher quality image transmission, image quality in the
same circumstances, the coding standard than the
traditional savings about 50% of the rate.
(2)the reasonable choice for some of the complexity of
the H.264 high performance, low-impact on the encoding
characteristics of the optimization, so that the system has
good real-time performance and stability.
At the same time, P4 class processor support MMx,
SSE, SSE2 instructions, etc., and these instructions for
achieving parallel processing to speed up computation
speed played an important role. Therefore, the full use of
processor resources, and the use of water mechanism,
rational design and scheduling the various modules of the
encoder, the H.264 codec to achieve the overall speed, but
also can improve the systems real-time effects[10].
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