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Compaq ProLiant 1600 Скачать руководство пользователя страница 8

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deliver very many streams for most network delivery. To achieve further reduction in data rate,
video compression is needed.

Compressing—Codecs

Different algorithms and techniques known as "codecs" have been developed for compressing
video signals. Video compression techniques take advantage of the fact that most information
remains the same from frame to frame. For example, in a talking head video, most of the
background scene typically remains the same while the facial expressions and other gestures
change. Taking advantage of this enables the video information to be represented by a "key
frame" with "delta" frames containing the changes between the frames. This is typically called
"interframe" compression. In addition, individual frames may be compressed using lossy
algorithms similar to JPEG photo-image compression. An example of this is the conversion from
RGB to the Y/C color space described above where some color information is lost. This type of
compression is referred to as "intraframe" compression. Combining these two techniques can
result in up to 200:1 compression. This compression is achieved through the use of a “codec”—an
encoder/decoder pair, depicted as follows.

Codecs vary depending on their purpose, for example, wide bandwidth vs. narrow bandwidth or
CD-ROM vs. network streaming. Encoders generally accept file types such as Audio/Video
Interleave (AVI) and convert them into proprietary streaming formats for storage or transmission
to the decoder. Multiple files may be produced corresponding to the various bit rates supported by
the codec. A codec may also be

asymmetric

or

symmetric

depending on whether it takes longer to

encode than decode. Some codecs are very compute intensive on the encode side and are used
primarily for creating content once that will be played many times. Symmetric codecs, on the
other hand, are often used in real-time applications such as live broadcasts. A number of codecs
have been developed specifically for CD-ROMs while others have been developed specifically for
streaming video.

Encoder

Decoder

Transmit

Store

A "Codec" is a combination of an En

Cod

er and a

dec

oder

100111001100010

Video In

AVI

QuickTime

Files

Streaming Files

Video Out

To Display

Proprietary

Streaming Codecs

Cinepak

Indeo

TrueMotionS

Smacker

Video 1

Power!VideoPro

Vxtreme

ClearVideo

VDOLive

Vivo

RealVideo

TrueStream

Xing

Proprietary

CD-ROM Codecs

MPEG

Codec Types

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Содержание ProLiant 1600

Страница 1: ...bers digital video has the advantage of not degrading from generation to generation and because it can reside on a computer disk it is easy to store search and retrieve It can also be edited and easily integrated with other media such as text graphics images sound music as well as transmitted without any loss in quality And now it is possible to deliver digital video over computer networks includi...

Страница 2: ...guration or configurations tested or described may or may not be the only available solution This test is not a determination of product quality or correctness nor does it ensure compliance with any federal state or local requirements Compaq Deskpro Compaq Insight Manager ProLiant Netelligent and SmartStart are registered with the United States Patent and Trademark Office Microsoft Windows Windows...

Страница 3: ...y peripheral vision which is not directed at the center of the retina is not as color sensitive For color sensing there are three types of cones capable of detecting visible light wavelengths It has been determined that a minimum of three color components e g Red Green and Blue corresponding to the three types of cones when properly filtered can simulate the human sensation of color Since color do...

Страница 4: ...ach called S Video is used in Hi 8 and Super VHS video cameras The RGB system separates the signal into three components Red Green and Blue and is used in color CRT displays Another approach to component video is to use Luminance Y Hue U and Saturation V as the three components Hue describes the color s shade or tone and saturation the purity or colorfulness of the color This approach dates back t...

Страница 5: ...sometimes on a disk in the camcorder itself Digital video from these sources may go directly to the hard drive of a PC by using an appropriate interface card The quality of digital video may be judged based on three main factors 1 Frame Rate The number of still pictures displayed per second to give the viewer perception of motion The National Television Standards Committee NTSC standard for full m...

Страница 6: ...te of 216 MegaBits per second Mbps This far exceeds the highest data rate achievable through most networks or across the bus of older PCs Until recently the only practical ways to get video on a PC were to play video from a CD ROM or to download a very large file across the network for playback at the user s desktop Neither of these approaches is acceptable for delivery of content across a network...

Страница 7: ...ly reduce the video rate as can be seen in the following diagram Even though the above scaling represents over a 10 1 reduction in data rate at the expense of size and video quality it is still not enough for most network delivery For example a 10BaseT Ethernet network supports data rates of 10 MegaBits sec This is not enough bandwidth to deliver even one video stream at the above scaled data rate...

Страница 8: ... This compression is achieved through the use of a codec an encoder decoder pair depicted as follows Codecs vary depending on their purpose for example wide bandwidth vs narrow bandwidth or CD ROM vs network streaming Encoders generally accept file types such as Audio Video Interleave AVI and convert them into proprietary streaming formats for storage or transmission to the decoder Multiple files ...

Страница 9: ...of the MPEG 1 standard described below H 263 H 263 was developed by the ITU in 1994 as an enhancement to H 261 for even lower bit rate applications It is intended to support videophone applications using the newer generation of PSTN modems at 28 8 Kbps and above It benefits from the experience gained on the MPEG 1 standard It supports five picture formats H 263 Resolutions Format Resolution Sub QC...

Страница 10: ...a rates of T1 lines MPEG 1 uses Interframe compression to eliminate redundant information between frames and Intraframe compression within an individual frame using a lossy compression technique similar to JPEG image compression Three types of frames result from the compression algorithm I frames P frames and B frames These are illustrated in the following diagram I frames do not reference other p...

Страница 11: ...orward fast reverse and random access into the bitstream However as mentioned above these access points are only at the I frame boundaries The CD ROM quality audio is stereo 2 channel 16 bit sampled audio at 44KHz The main MPEG 1 resolution of 360 x 242 is called Standard or Source Input Format SIF and unlike the Common Intermediate Format CIF defined earlier differs for NTSC and PAL systems The c...

Страница 12: ...minals video email wireless mobile video devices and interactive home shopping It was originally designed to support data rates of 64Kbps or less but recently has been enhanced to support a wide range of bit rates from 8 Kbps to 35 Mbps This enables it to support both consumer and professional video with a variety of resolutions corresponding to the H 263 video conferencing standard discussed earl...

Страница 13: ...te copy does not have to reside on the user s hard drive Another advantage is that video content may be integrated and streamed along with other media and the video can play inside standard Web browsers The following diagrams contrast the download and play model with the new streaming model Delivering video by the download play method involves transmitting the complete file e g in AVI format to th...

Страница 14: ...equence numbers in the video data packets so they can be properly assembled and played out of the receiving buffer Over IP based networks such as the Internet a new protocol called Real Time Protocol RTP has been developed to accomplish this Video Streaming System A complete video streaming system involves all of the basic elements of creating delivering and ultimately playing the video content Th...

Страница 15: ...nection The video server consists of a hardware platform that has been optimally configured for the delivery of real time video plus video server software that runs under an operating system such as Microsoft Windows NT that acts as a traffic cop for the delivery of video streams Video server software is generally licensed by the number of streams If more streams are requested than the server is l...

Страница 16: ...sion of video over a network is the ability to support multicasting broadcasting and unicasting of video streams Multicasting lies between broadcasting and unicasting Unicasting delivers streams 1 to 1 to each client and is sometimes referred to as Video on Demand VoD since any user can request any stream at any time Multicasting by contrast delivers streams simultaneously 1 to many clients where ...

Страница 17: ...a If a data collision occurs all contending nodes back off and re transmit after a random delay This enables shared Ethernet to support a large amount of bursty data traffic corresponding to multiple shared applications and devices such as modem communications sending and receiving faxes printing accessing corporate databases such as phone directories and group calendars internal and external e ma...

Страница 18: ...ckbone The next generation of Fast Ethernet Gigabit Ethernet is in development ATM Asynchronous Transfer Mode uses hardware switching to provide not only high speed 25Mbps to 2 5Gbps but it also a guaranteed Quality of Service QoS and multicasting through a circuit switched connection It uses fixed 53 byte packets and was designed from the outset for multimedia data transmission such as video soun...

Страница 19: ...media data streams such as video It supports multicasting authentication encryption and a larger address space Since it can t be rolled out everywhere at once it is intended to be backward compatible with IPv4 MBONE The Multicast Backbone is an experimental overlay network on the Internet to gain experience with multicasting that will be supported in IPv6 There are approximately 1700 networks in 2...

Страница 20: ...itize specific packet streams It does this by requesting the dynamic allocation of bandwidth from the network much like PC applications dynamically allocate memory for applications Public Broadband Networks Telecommunications deregulation has enabled local and long distance carriers to compete with each other as well as with cable TV operators for long distance services as well as value added serv...

Страница 21: ...WHITE PAPER cont 21 ECG068 0798 ...

Страница 22: ... to multiple clients sending the same video to several clients simultaneously or sending different videos to individual clients at the same time q Transmitting video over the network reading buffering formatting packetizing and sending data over the network using the specified network protocols q Storing video data providing fault tolerant support q Detecting abnormal client termination e g power ...

Страница 23: ...gh capacity high performance disk drives for storing and delivering real time video content q High performance network cards such as 10 100BaseT ATM for high bandwidth network connections q Fast system and I O busses such as PCI and Wide Ultra SCSI q Tuned device drivers for network cards and disk access q Multiple high performance CPUs that can be dedicated to uninterrupted video delivery q Large...

Страница 24: ...ys with controllers that support content striping For example wide Ultra SCSI 3 disk controllers provide a sustainable throughput of 40 MB sec twice that of Fast Wide SCSI 2 For some applications the availability of high rotation speed disks e g 10 000 rpm is also desirable for maximum performance High Performance Network High quality broadcast video can be delivered at bit rates ranging from 3 Mb...

Страница 25: ...f concurrent streams they can deliver the cost per stream is often an important measure of video server efficiency This parameter can be a misleading comparison however if it fails to take into account the above important hardware characteristics which also have a cost impact Nevertheless the best cost per stream is more likely to come from the ranks of high volume industry standard architectures ...

Страница 26: ...oLiant 5500 can be expanded from 128 MB up to 3 GB for handling high workloads of multiple concurrent video streams q High availability options To maximize availability with minimum downtime the ProLiant 5500 supports hot pluggable redundant components such as power supplies disk drives fans and network interface cards q Large number of expansion slots There are 5 PCI and 3 shared EISA expansion s...

Страница 27: ...phic Experts Group LBR Low Bit Rate MBONE Multicasting BackBONE Mbps Megabits per second MJPEG Motion JPEG MPEG Motion Picture Experts Group NIC Network Interface Card NTSC National Television Standards Committee U S TV standard NVOD Near Video on Demand PAL Phase Alternation Line European TV standard PCI Peripheral Component Interconnect PSTN Public Switched Telephone Network QoS Quality of Servi...

Страница 28: ...oks q Video and Media Servers Technology and Applications Focal Press Karl Paulsen 1998 q Publishing Digital Video Academic Press Jan Ozer 1997 q A Technical Introduction to Digital Video Charles A Poynton John Wiley Sons 1996 q Digital Video An Introduction to MPEG 2 Haskell et al Chapman Hall 1997 q Video Dialtone Technology Daniel Minoli McGraw Hill 1995 q The Digital VideoMaker s Guide Kathryn...

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