MPEG2_intro_v02_GB

1、MPEG2 / DVB概述1数字与模拟的比照模拟有限的带宽1 个频道l = 1 个电视节目多种标准PalSecamNTSC有限的质量复合视频 (减少色度 resolution)数字增加的带宽1 频道 = 多达 12 个电视节目单一标准DVB新的电视业务互动电视按次付费PPV视频点播VOD改进的质量复合视频 (no cross color effect)立体声音频和环绕立体声2视频数字化3CCIR 601 建议书模拟视频信号传达了许多信息，例如:水平同步垂直同步Test linesCCIR 601 标准定义了如何使用对运动的视频进行编码8bits 亮度和色度，根据4:2:2格式与625/50 和

2、 525/60 标准兼容与以上两个标准的采样数相同4Active Field1Active Field2VBI Field 1VBI Field 2HANCField288 lines240 lines288 lines240 lines24 lines25 lines625 lines525 lines2720 samples(720 Y + 2360 Cr,Cb)2144 samples非压缩数字视频 4 : 2 : 2YCrCb13.5 MHz6.75 MHz6.75 MHz复合27 MHzx10 bits/采样 = 270 Mbit/sx8 bits/采样 = 216 Mbit/s16

3、6 Mbit/s active5A:B:C Notation6DVB 标准DVB-S卫星数字传送系统DVB-C有线数字传输系统 DVB-T地面数字播送系统DVB-SI业务信息标准DVB-CA条件接收通用接口DVB-RC有线电视系统回传通道其他7MPEG 概述MPEG : 运动图像专家组, 创立于 1988MPEG Group 负责音频和视频压缩标准的制定199219941996JPEG : CCITT 建议书 H261 静态图像 DCT 转换 Huffman 编码 可变比特率 (Openloop)MPEG-1 : ISO/CEI 11172 视频 JPEG 功能 1.5 Mb/s max On

4、ly SIF (360 x 288) 媒体存储MPEG-2 : ISO/CEI 13818视频 MPEG1 兼容 10Mb/s HD 格式 广播目的8MPEG 2普通标准视频编码 (ISO/IEC 13818-2)音频编码 (ISO/IEC 13818-3)系统 (ISO/IEC 13818-1)应用多样性纪录和存储 : Beta SX, DVD播送 : DVB网络传送 : ATM格式兼容性采样率 : 4:4:4, 4:2:2, 4:2:0分辨率 SIF to HDTV逐行和隔行扫描Mutiscale extensionprovides multiquality transmission :

5、basic + enhanced9MPEG 采样模式F1/L1F2/L1F1/L2F2/L2Fn/Ln : Frame/lineCB, CR samplesY sample4:4:4 采样(24 bits / pixel)F1/L1F2/L1F1/L2F2/L24:2:2 采样(16 bits / pixel)F1/L1F2/L1F1/L2F2/L24:2:0 采样10Principe du traitement intra-trame (JPEG)原始图像Yu,vYQu,vYZZxYRLCx压缩的图像72727273737472727372726975757466DCT量化Zig-Zagsc

6、anCodage longueur variableCodage entropique57114-23-5-1-1-1300000-1036100-1000000000003610-100036012-100100110101111010.Bloc11空间相关 : DCT离散余弦变换 系数Maximum energy DC component mean block value像素块以它所在的空间位置的亮度值表示Matrix of DCT coefficientsrepresenting frequency components in theblockMinimum energy maximum

7、 spatialfrequencyHorizontal frequencyVertical frequency12时间相关 : 运动补偿InterpolationMotionvectorBBIP13MPEG 视频序列的层 / 时间图像(p slices)Slice(n macroblocks)宏块(4 blocks)块(8 x 8 pixels)II图像组 (GOP)序列14图像组 : GOPM = 3 imagesN = 12 imagesI1B2B3P4P7B5B6P10B8B9B11B12I13forward predictionbidirectional predictionIntra

8、 Images (I) : 参考图像, 用 DCT编码Predicted Images (P) :使用前面的图像编码(I or P) ，使用运动补偿向量Bidirectional images (B) :使用前面和后面图像进行插值 (I or P)15图像顺序I1B2B3P4P7B5B6I10B8B9B11B12P13I1B-1B0P4P7B2B3I10B5B6B8B9P13表示顺序传送顺序图像组 (N=10 / M=3)16MPEG 视频编码器框图Source pictureQuantizationstep预处理(Format, picture ordering)DCTQMux& VLCBu

9、fferEncodedpicturePredictionerrorIDCTIQIntra/Inter/Bidir.modesDecision0motionvectorsMotioncompensationPicturememoryMotionestimationPrediction17MPEG-2: Profiles & LevelsMPHLMPH14LMPMLSPMLSNRPMLSSPH14LHPHLHPH14LHPMLMPLLSNRPLL18视频流缓冲I0P3B1B2P6B4B5P9B7B8I12Buffer levelTimeMaxI,P,BEncodingBufferBit Rate

10、CTRLBufferI,P,BDecodingSource PicturesVideo Stream(constant bit rate)Decoded PicturesI10Decoding Time (DTS)Presentation Time (DTS)CoderDecoder19MPEG 音频 : the digital chainFILTER(BWKHz)ADCFe 2BWKHz(采样频率)QUANTIZING&CODINGS(t)S(n)FeDECODINGS(t)S(n)STORAGEMEMORYBit Rate 采样 : 16 bits 频率 : 32, 44.1, 48KHz

11、 信噪比 : 96dB 频带宽度 : 15/20KHz 比特率 : 2x768kb/s数字音频磁带 采样 : 16 bits 频率 : 44.1KHz 信噪比 : 96dB 频带宽度 : 15/20KHz 比特率 : 2x705.6kb/sCD光盘DAC20MPEG 音频 : 量化错误S(t)tS(t)tt BW/2模拟信号数字信号Vt The sampling process introduces the Quantizing NoiseQuantizing noise (SNR) = 6.02n + 1.76 dBex : SNR = 98.1dB for a 16 bit system0

12、00001010011100QuantizingInterval QMax. error : +/- Q/221MPEG 音频 : 16位采样的量化噪声-10dB-50dB-100dB频率 (kHz)音频信号频谱-140dB量化噪声5101520信噪比(SNR) = 6x16 = 96 dB22MPEG 音频 : 3位采样的量化噪声-10dB-50dB-100dBFrequency (kHz)音频信号频谱-140dB5101520量化噪声可听见的噪声 !信噪比(SNR) = 6x3 = 18 dB23MPEG 音频 : 心理声学模型 (1)020406080dB可闻域在安静环境下的可闻域205

13、01005001K2K5K10K20Kf(Hz)不可闻的可闻的24MPEG 音频 : 心理声学模型 (2)020406080dBThreshold of audibilityThreshold of audibilityat silence20501005001K2K5K10K20Kf(Hz)pure 1Khz sinusmasking threshold25MPEG 音频 : 量化错误的调整-10dB-50dB-100dB频率 (kHz)Masking Threshold音频信号频谱THE QUANTIZING ERROR IS ADJUSTED FOR EACH SUB-BAND750 H

14、z024KHz26MPEG音频 : BIT ALLOCATION-10dB-50dB-100dBFrequency (kHz)5 bits2 bits0 bitSUB-BAND BIT ALLOCATIONSCALE FACTOR (maximum value during 8ms)TOTAL DESIRED BIT RATETHE ALLOWED QUANTIZING NOISE 27Principle behind the MPEG-1 audio encoderPsycho-acoustic model32 filterbankMultiplexerControlMPEGaudiostr

15、eam PCMinputLRQ1Q32Q3Q2Quantisation28MPEG-2 (MPEG-1 兼容)环境 编码/解码原理MatrixMPEG-1audiodata Left LRight RCoderLeft surround LSCentre CRight surround RSMPEG-1encoderMPEG-2extensionencoderMPEG-2auxiliarydata TransmissionL0R0T3T4T529MPEG 音频: 音频包30MPEG 2 层次结构31MPEG2 节目与传送流复用Program streamPS MuxProgramme NVid

16、eo coderISO/IEC 13818-2Audio coderISO/IEC 13818-3Time baseSTC NVideo coderISO/IEC 13818-2Audio coderISO/IEC 13818-3Time baseSTC 1PacketizerPacketizerTSMuxSystem coderISO/IEC 13818-1Programme 1Transport streamHard diskQuasi error-free mediaDVDError-prone mediaVideo dataAudio dataVideo dataAudio dataP

17、ES VideoPES AudioPCRPacketizerPacketizerPES VideoPES Audio32打包的根本流(PES)的创立830 kbytes830 kbytes830 kbytes830 kbytesMPEG-2 编码打包有效负荷包头源视频打包的基本流fixed lengthPresentation Units(uncoded pictures)variable lengthAccess Units(coded pictures)fixed or variable length PES packets33PES的组成 (main fields)MPEG-2 PES1

18、011.1100 : PSM1011.1101 : private data T11011.1110 : Padding stream1011.1111 : private data T2 110 x.xxxx : audio (1 to 32)1110.xxxx : video (1 to 16)1111.0000 : ECM1111.0001 : EMM.Stream id (8)包起始码stream idPES 包长可选的l PES 包头PES 包数据包头有效负荷10PES scrambling controlPES prioritydataalignmentindicatorcopyr

19、ightoriginalor copy7flagsPES headerdata lengthoptionalfieldsstuffingbytes(0 xFF)E.g. stuffing bytes incase of PES at fixedlength)PTSDTSESCRESrateDSMtrick modeadditional copy infoPreviousPES CRCPES extensionPES extensionfield lengthP-STDbufferscale & sizeprogram packetseq entrpackheaderlengthPESpriva

20、te dataPES extensionfield dataoptional fields5flags00 : no scrambling01 : no scrambling 10 : scrambling with an even control word11 : scrambling with an odd control word (hierarchical system forexample)Bit rate of PESPresentation and decodingtime stamps expressed in 90 KHz clock periods(maximum dela

21、y between 2broadcast = 0.7 s)packet start code prefixstream idpacket lengthSTD Buffer scale & size PTSDTSstuffing bytes data bytesMPEG1 PES00.00.01h34TS 包的构建PES 包TS 包填充域(填充字节)188 bytes(包头 + 有效负荷)35MPEG2 Transport Stream Paquets36MPEG2 传送流语法1 if the payload information is erroneous.Example: demodulat

22、ed signal (QPSK), when the external code (RS) and internal code (convolutive) are not able to correct the errors.包头adaptationfield (*)payload188 BytesStuffing at case of TS endsplicetypepiecewiserate ItwoffsetItw_validflagDTS_next_au00 : No scrambling01 : Scrambling the default control word10 : Scra

23、mbling an even control word11 : Scrambling an odd control word the same as the PES onesyncbytetransport errorindicatorpayloadunit startindicatortransport priorityPIDtransportscramblingcontroladaptation fieldcontrolcontinuitycounterPCR counterIdentifier of the component defined by the operator.PID=0

24、(PAT table) andPID=0 (CAT table) are reserved values.1 if the payload begins:with a PES start (the PES 1st byte has to begin at a payload start).with a PSI table start.Payload begins with a pointer-field which indicates the position of the PSI table 1st byte.47hoptionalfieldsstuffingbytes5flagseleme

25、ntarystream priorityindicatorrandomaccessindicatordiscontinuityindicatoradaptationfieldlength(*): non systematicPCROPCRsplicecountdowntransportprivate data lengthoptional fields3flagsadaptationfield datalengthtransportprivate data length37节目参考时钟 (PCR)PCR is used to recover the program encoding clock

26、 at the decoder sitePCR are generated for each program stream, and the TS packet which carry the PCR are identified in the PMT table, with a specific PID (PCR_PID)PCR_Base consists of 33 bits (n x 90 kHz)PCR_Extension consists of 9 bits (m x 27 MHz) PCR is inserted into the Adaptation field of some

27、TS packets (at least every 0.1 seconds)At any time the TS stream is modified, PCR must be updated !27 MHzPCRStreamEncoder Time Stamps InsertionVCXO(27 MHz)PCRStreamDecoder program clock recoveryPCRProcessingDVBChain38MPEG2-PSI : Program Specific Information (2)neverencryptedUsuallyencrypted1 or seve

28、ral sectionsPID 0PID 0PID 1PID 10PID 10PID 32PID 1201 or several sectionsPAT(PID 0)ServicesPID ofPMTService 0Service 1Service 2Service 7103268147NIT(PID 10for example)Private dataCAT(PID 1)CAPIDCA syst 1 CA syst 2 CA syst 31201301401 sectionPMT of service 1(PID 32)ComponentsPIDVideo CA_Descriptor.Au

29、dio (F) CA_Descriptor.Audio (E)Audio (G)Sub-title730129501315257103PID 120 = EMM syst 1PID 32 = PMT service 1+ PMT descriptors1 or several sections39DVB-SI : 网络与复用概念TSTSTSTSTSTSTSTSTSTSTSTSffTSTSTSTSTSTSf36 MHz Transponders8 MHz channels8 MHz channelsSatelliteCableTerrestrialNetworksMultiplexesServi

30、cesBouquetComponents40DVB 条件接收加扰器ECM发生器EMM发生器解扰器CW发生器ECM接收EMM接收ECM控制层EMM管理层CW（控制字）CW（控制字）业务数据业务数据业务密钥- 业务密钥- 接收条件- 业务密钥- 管理密钥- 用户权限- 管理密钥- 用户权限41EMM 和 ECM 在传送流中发现的处理方法Prog 3Prog 3PID 0Video 3PID MECM-3EMM-1PID 1Video 3Audio 3EMM-2CA System 1CA System 2EMM-1 referenceEMM-2 referenceCATsectionsPATsect

31、ionsPMTsectionsPIDAudioVideoECMPCRPID M传送流42信息管理系统4355 Mb/s27.5 MHz(x 2)(x 1.28)35.2 MHz38 Mb/s41.25 Mb/s(TS=188 TS with RS = 204)(Puncturing 3/4)Channel EncodingQPSK Modulation MPEG-2/DVBSignalIF70 MHzBW = 35.2 MHz1/2 Nyq.FiltersD/AD/AQPSKmodulationEnergy dispersal(PRBS)Outercoding(RS)InterleavingI

32、nner coding(convolutionand puncturing)7 Mb/s8 MHz38 Mb/s42 Mb/sroll-off = 0.15MPEG-2/DVBSignalIFBW = 8 MHzDifferentialencodingD/AD/AQAMmodulationEnergy dispersalRSInterleavingByte to symbolConversionChannel EncodingPhysicalInterfaceClockDataQAM ModulationI, Qseparation1/2 Nyq.FiltersLOValues (exampl

33、e)信道编码和调制卫星调制Cable 调制44调制 : 64 QAM45调制: 调制质量46有线调制: 比特率47完整的DVB传送和接收链Programme 1MPEGcodingMultiplexing+ scramblingFEC, formattingfiltering, DACQAM or QPSKmodulationPESMPEGcodingMPEGdecodingDescrambling + demultiplexingADC, filtering, formatting, FECQAM or QPSKdemodulationUp-conversion, amplification

34、CABLE or SATELLITEAmplification down-conversionProgramme nPictureSoundPES188 bytepacket188 bytepacket112I, QIFPESIFI, QChannel coding/decoding345678910Source coding/decodingSelection48DVB-S 典型系统结构UpLink Station Satellite OperatorQPSK ModulatorQPSK ModulatorQPSK ModulatorDigital Broadcasting CentreMPEGASIRouterOPEN TVServerATMTXATMRXNVODServerATMTXOFDMReceiverDescramblerQPSK ReceiverDescramblerPLAY OUTCENT