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Introduction to MPEG-2 Compression and Transport Streams November 2002 Dennis Kucera

DVB Overview. Introduction to MPEG-2 Compression and Transport Streams November 2002 Dennis Kucera Tektronix, Inc. The Digtal Video Broadcasting Initiative.

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Introduction to MPEG-2 Compression and Transport Streams November 2002 Dennis Kucera

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  1. DVB Overview Introduction to MPEG-2 Compression and Transport Streams November 2002 Dennis Kucera Tektronix, Inc.

  2. The Digtal Video Broadcasting Initiative • DVB Project was founded in Europe in 1993 as an industry led consortium of 290 broadcasters,manufacturers s/w developers & regulatory bodies in 35 countries to adopt a standard for digital broadcasting that would bring more programme choice to the home at an affordable price and with efficient use of the frequency spectrum. • The US FCC adopted the major elements of the ATSC Digital Television Standard (A/53) in 1996 for the nation's next generation of broadcast television. Similar aims to DVB but with more emphasis on HDTV at the outset. • The Japanese Ministry of Posts and Telecommunications followed suit and launched the BS-Digital standard for satellite transmission as first step towards the Integrated Services Digital Broadcast (ISDB) network.

  3. The European DVB Project • Set up to address:- • Transmission Standards • Modulation Systems • Error Correction • Integrated Receiver/Decoders (IRD) • Service Information that were not covered by MPEG-2 • Now adopted world-wide • See DVB V2.0 CD-ROM (www.DVB.org)

  4. What is DVB? DVB RF DVB IF DVB FEC – R/S DVB PI DVB Testing DVB SI MPEG-2 MPEG-1 VHF, UHF, L-Band DVB S, C, T (QPSK, QAM, COFDM) FEC – R/S EN 50083-9 V2 DVB SPI, ASI, SSI TR 101 290 Timing and Protocol Testing EN 300 468 DVB Service Information (EPG) ISO/IEC 13818-1,2,3 MPEG-2 Systems, Video, and Audio ISO/IEC 11172-1,2,3 MPEG-1 Systems, Video, and Audio

  5. DTV Transmission Chain Programme Specific Information(PSI) or Service Information (SI) ES=Elementary Stream containing Access Units I,B,P Timing DTS/PTS Data System Time Clock (STC) M U L T I P LEXER M O D U L A T O R ES Packetiser Encoder PES Video Packetiser PES Presentation Units Data Transport Stream PES Packetiser Encoder Audio ES Packetiser PES ??? DVB ATSCISDB MPEG Compression Layer MPEG Systems Layer+ DVB/ATSC/ARIB 13818-2 A/53 atsc 13818-3 A/52 ac3 13818-4 13818-1 ETS 300-468 A65 PSIP 13818-4 ETR 290 ETR154 A54 QPSK , OFDM QAM HM 8VSB Basic Standards

  6. The Standards • The MPEG-2 video compression standard and transport mechanism are common to DVB, ATSC & ISDB. • Three audio compression standards are in use namely MPEG-1&2, Dolby AC3 and AAC. • There are three Service Information standards namely DVB SI, PSIP (USA) and ARIB SI ( Japan) There is no definition of quality in any of these standards. The key word is interoperability between the various components of the digital broadcast chain.

  7. MPEG-2 Core Standards • ISO/IEC 13818-1 (systems) • Transport Stream and PES syntax • T-STD Buffer model (decoder) • PSI definition (PAT,PMT, CAT,NIT) • Definition of PCRs, PTS and DTS • ISO/IEC 13818-2 (video coding) • Uses MPEG-1 as base syntax for Sequence, GOP, Picture, Slice and Macro Block syntax • Five coding Profiles and four source formats or Levels • Coding on frame or field basis-interlace.

  8. MPEG-2 Core standards • ISO/IEC 13818-3 (audio coding) • Builds upon ISO/IEC11172-3 (MPEG-1) • Defines extensions for Multichannel audio and lower sampling frequencies • Very rare usage? • ISO/IEC 13818-6 (DSM-CC, 1996 addition to MPEG-2)) • User-to-User functionality • User-to-Network functionality • Basis for Data Broadcast

  9. Base Band Standards • EN 500083-9 Interfaces for CATV/SMATV headends and similar professional equipment

  10. DVB Transmission Standards • Satellite DVB-S • Cable: DVB-C • Terrestial: DVB-T

  11. Test Standards • MPEG • ISO/IEC 13818-4 (conformance) Baseband only. • DVB • TR101 290 Baseband and Transmission Measurement • ATSC • A64 Transmission Measurement and Compliance.

  12. ATSC Standards (www.ATSC.org) • A/52 - Digital Audio Compression (AC-3) Standard • A/53 - ATSC Digital Television Standard • A/54 - Guide to the use of ATSC digital Tv standard. • A/55 - Programme Guide for digital TV • A/56 - System in formation for digital TV. • A/57 - Program/Episode/Version Identification Standard • A/58 - Harmonisation with DVB SI in the use of ATSC. • A/63 - Standard for coding 25/50 Hz video. • A/64 - Transmission measurement and compliance. • A/65 Rev A 24 Feb00 - Program and System Information Protocol for Terrestrial Broadcast and Cable . • For Terrestrial Broadcast and Cable A/65 replaces: • A/55 - Program Guide for Digital Television • A/56 - System Information for Digital Televisionwhich remain valid for satellite. • A/90 - Data Broadcasting • A/91 - Implementation guidelines for data.

  13. ISDB Standards • Satellite • ARIB STD-B20 System • SRIB STD-B21 Receivers • ARIB STD-B25 CA • ARIB STD-B10 Service Information • ARIB STD-B24 Data Coding • Terrestrial • To be drafted System • To be drafted Receivers • Other standards as for satellite. • Cable Draft

  14. MPEG- 2 Formats

  15. The 4:2:2 Profile • Intended for professional video applications where ease of editing and multi generation coding /decoding of video are important. • I pictures are necessary which also result in high coding bit rates. • It supports both 4:2:0 and 4:2:2 formats. High profile could handle this bit but decoder expensive because of other bells and whistles in the profile. • 4:2:2 profile is compatible with the Main Profile. • Maximum bit rate = 50 Mbit/s (300 Mb/s for HD)

  16. ATSC Formats ML@MP differs from MPEG in that progressive scan above 30 frames is allowed and input does not correspond to CCIR 601. Higher level formats chosen to create square pels at !6:9 If a CCIR 601 input 720 x 483 input is received, only 480 of the 483 active lines are used for encoding. Only 704 of the 720 pixels are used for encoding. The first eight and the last eight are dropped.

  17. DTV Transmission Chain Programme Specific Information(PSI) or Service Information (SI) ES=Elementary Stream containing Access Units I,B,P Timing DTS/PTS Data System Time Clock (STC) M U L T I P LEXER M O D U L A T O R ES Packetiser Encoder PES Video Packetiser PES Presentation Units Data Transport Stream PES Packetiser Encoder Audio ES Packetiser PES ??? DVB ATSCISDB MPEG Compression Layer MPEG Systems Layer+ DVB/ATSC/ARIB 13818-2 A/53 atsc 13818-3 A/52 ac3 13818-4 13818-1 ETS 300-468 A65 PSIP 13818-4 ETR 290 ETR154 A54 QPSK , OFDM QAM HM 8VSB Basic Standards

  18. Transport Stream Packets • Fixed length of 188 bytes • Packets contain one type of data only i.e video,audio, data, programme guide information. • May also carry timing information (PCR) • Every 4 Byte Header Contains following fields: • sync byte 0x47 • transport error indicator • payload unit start indicator 188 Byte Packet 4 Byte Packet Header Adaptation Field (if present) Payload (if present)

  19. Transport Packets • Transport priority • PID • Scrambling Control • Adaptation field control • Continuity Counter. • Adaptation field used either for stuffing or for information. This is only stuffing method allowed for transport packets carrying PES packets. • In transport packets carrying PSI information stuffing bytes of value 0xFF placed after the last byte of a section of information to the end of the packet. • Null Packets

  20. The Packet Header

  21. Programme Guide Information • PSI - Programme Service Information. This is defined by MPEG and consists of PAT,PMT,CAT,NIT,TSDT • SI - Service information. These are additional tables defined by DVB (eg SDT,TDT,EIT etc) (two categories Mandatory & optional) • PSIP - Additional tables defined by ATSC for terrestrial and cable only (MGT,VCT etc) • ARIB SI- Additional tables defined by ARIB in Japan for satellite.

  22. PSI Information-the table structure PID 0 Programme Association Table - PAT NIT PID 16 Network Information Table Prog 0 PID16 Prog 1 PID 20 PID20 Prog 2 PID 30 PID 30 Programme Map table PMT Programme Map table PMT Stream Type PID Stream Type PID 1 Video 19 1 Video 50 2 Audio 33 2 Audio 42 3 Audio 29 3 Audio 35 0 20 30 19 35 33 50 42 PID No. PAT Prog 1 PMT Prog 2 PMT Prog1 Vid1 Prog2 Audio2 Prog1 Audio1 Prog2 Vid1 Prog2 Audio1 Prog 1 Audio2 Transport Packets

  23. Program Clock Reference (PCR) • What it does • Enable the MPEG decoder to synchronise to the encoder. • How it does it • 42 bit sample of the STC at the encoder indicates to the demultiplexer what the STC time should be at the decoder when each clock reference is received. • Synchronisation errors arise if the PCR value generated by the multiplexer is inaccurate or if it is received late because of network delays e.g Jitter. System Time Clock (STC) PCR

  24. PCR Value PCRn =PCR base + PCR extension Tn = PCR base / 90x103+ PCR ext / 27x106 = 300x PCR base / 27x106+ PCR Extension/ 27x106The PCR value displayed by Adherent represents the number of cycles of the 27Mhz clock each of duration 37nSec. i.e. clock ‘ticks’ 90x103 Hz Modulo 300 27x 106Hz Counter 233 PCR extension PCR base

  25. PCR Tolerances • Decoders use PCRs to generate video timing And sometimes colour burst . Therefore there are strict limits on PCR repetition rate, accuracy . • The recommended repetition rate is between 40-100ms • PCR inaccuracy must be less than +/- 500 nS

  26. Overall Timing Jitter Overall Jitter = PCR Inaccuracy + PCR Arrival Time Jitter ClockFrequency Countererror VariableNetworkDelay Clockdrift Re-multiplexing

  27. The PLL Subtractor LP Filter VCO PCR Subtractor VCO Load Counter Counter System Time Clock Encoder Path Delay Decoder Encoder STC Enc. STC Dec. STC PCR1 0 sec 1sec 1 sec 0 sec PCR2 .1 sec 1.1 sec .1 sec PCR3 .2 sec 1.2 sec .2 sec No timing Jitter

  28. Decoder Buffer(T-STD) • hh Decoder control via PTS/DTS Video Data buffer Video Decoder Re-order buffer MPEG 2 TS System demuxand extract PCR STC Generator STC Decoder control via PTS/DTS Audio Data buffer Audio Decoder

  29. Delay VideoTS Packets AccessUnits Transport Buffer MultiplexBuffer Elementary Decoder Buffer Video Decoder Decoded PresentationUnits Transport Buffer Elementary Decoder Buffer AccessUnits Decoder Decoded PresentationUnits Transport Buffer sys Elementary Decoder Buffer sys Systemdata T-STD Buffer model TSPackets

  30. The need to test digital TV To ensure interoperability between all the components of the DTV broadcast chain during the development, deployment operation and maintenance phases.

  31. DTV in regions of the world • DVB adopted in Europe and parts of Asia. Uses MPEG1&2 or Dolby AC3 audio. • ATSC adopted in the USA and parts of Asia. Same principles as DVB but focused on HDTV single programme per RF carrier, Uses Dolby AC3 audio. • Japanese ISDB followed on with similar aspirationsbut with HDTV and standard definition in one system.Uses MPEG AAC advanced audio coding (like MPEG4)

  32. Audio compression systems usedin MPEG-2 transport streams • MPEG-1 layers 1, 2 & 3 (Europe & DVB domain) • layer-II used in broadcast systems • MPEG-2 audio (5.1 channels) possible, but rarely used • All are ‘backwards compatible’ • Dolby digital (AC3) USA ATSC and also DVB (Germany) • 5.1 channels (0.1 = low freq effects) • AAC (Japan) ADIFF and ADTS type audio • MPEG-4 will use AACas default standard (Frauhoffer labs) 8 or more channels dynamically reposition-ablein space

  33. DVB Overview Testing VidTrans October 2002 Dennis Kucera

  34. Types of Errors Priority • Errors that prevent decodability 1 • Errors which impair decodability 2 • artifacts in the decoded picture • intermittent decoding • Errors that indicate a problem 3 at the encoder or multiplexer but do not affect decodability

  35. Test Documents • MPEG • 13818-4-MPEG • Covers all layers ES to TS • DVB • 13818-4 and • TR101 290-DVB • Covers Systems Layer only + RF • Refers to 13818-1, TR101 211, ETS 300,468 and others. • ATSC • 13818-4 • A54,A65

  36. So, what more are the broadcasters asking for? What does this mean?…..

  37. Templates- definition • A Template profile consists of a unique combination of tests, defined by a user, depending on his particular custom monitoring needs. • The tests forming the part of a template profile can encompass standard tests [TR101290] and proprietary tests. • Each ‘template applied’ test can have maximum, minimum or ‘window’ parameter range associated with it.

  38. Template Profile example Template Profile 1 • Network ID: 9018 (0x233A) • Transport Stream ID: 16640 (0x4100) Service Ids • 4164 Monrovia News-48 • PIDS • 101 Video with PCR • 102 Audio • 105 DVB Subtitle • 4228 Widgets Interactive channel • PIDs • 610 Video with PCR • 611 Audio • 720 DSMCC object carousel

  39. TR101 290 • Baseband measurements split into 3 groups • 1st priority • 2nd priority • 3rd priority

  40. TR101 290 1st Priority No:Indicator 1.1 TS_sync_loss 1.2 Sync_byte_error 1.3 PAT_error 1.4 Continuity_count_error 1.5 PMT_error 1.6 PID_error

  41. TR 101 290 2nd Priority No:Indicator 2.1 Transport_error 2.2 CRC_error 2.3 PCR_error 2.4 PCR_accuracy_error 2.5 PTS_error 2.6 CAT_error

  42. TR 101 290 3rd Priority No:Indicator 3.1 NIT_error 3.2 SI_repetition_error 3.3 Buffer_error 3.4 Unreferenced_PID_error 3.5 SDT_error 3.6 EIT_error 3.7 RST_error 3.8 TDT_error 3.9 Empty_buffer_error 3.10 Data_delay_error

  43. PSI - PAT, PMT tests • For the PAT TR 101 290 specifies • Repetition rate of PID 0 less than 0.5s • Scrambling control set to 00 (unscrambled) • PID 0 must contain only PAT sections • For a PMT TR 101 290 specifies • Repetition rate less than 0.5s • Scrambling control set to 00 (unscrambled)

  44. PCR measurements • TR101 290 measurements • PCR_error • Discontinuity of > 100 ms • Repetition rate • PCR_accuracy_error • Accuracy of encoded PCR values

  45. In-Service Monitoring • Continuous monitoring for 24 hours a day, 365 days a year • Required by: • Broadcasters • Regulators • Service providers

  46. In service monitoring system requirements • Comprehensive real time monitoring • Remote control • Logging of faults • Variety of interfaces • Simplified User Interface

  47. Monitoring parameters • TR101 290 1st, 2nd and 3rd Priority • Bit rate • Templates

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