Introduction to MPEG2 Transport Streams

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,manufa
  cturers 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)
ESElementary Stream containing Access Units
I,B,P
Timing DTS/PTS
Data
M U L T I P LEXER
System Time Clock (STC)
M O D U L A T O R
Encoder
Packetiser
ES
PES
Video
Packetiser
PES
Presentation Units
Data
Transport Stream
PES
Encoder
Packetiser
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-12, 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

• TR 101 154 Systems Implementation guidelines
• Coding and decoding
• Minimum receiver functionality
• Really an extension of 13818-1

10
Base Band Standards

• ETS 300 468 SI specification
• Defines the SI table mechanism
• Defines the SI tables
• Defines the descriptors
• TR 101 211 SI Implementation guidelines
• Defines rules of operation
• TR 101 162 Allocation of SI codes for particular
  broadcasters

11
Base Band Standards

• EN 301 192 Specification for Data broadcasting
• Defines 5 data broadcasting profiles (extractions
  from 13818-6)
• TR 101 202 Implementation Guidelines for data
  broadcasting
• Rules of operation for data broadcasting

12
Base Band Standards

• EN 500083-9 Interfaces for CATV/SMATV headends
  and similar professional equipment

13
DVB Transmission Standards

• Satellite DVB-S
• Cable DVB-C
• Terrestial DVB-T

14
Test Standards

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

15
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 Television
  which remain valid for satellite.
• A/90 - Data Broadcasting
• A/91 - Implementation guidelines for data.

16
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

17
MPEG- 2 Formats
18
The 422 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 420 and 422 formats. High
  profile could handle this bit but decoder
  expensive because of other bells and whistles in
  the profile.
• 422 profile is compatible with the Main
  Profile.
• Maximum bit rate 50 Mbit/s (300 Mb/s for HD)

19
ATSC Formats
ML_at_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 !69
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.
20
DTV Transmission Chain
Programme Specific Information(PSI) or Service
Information (SI)
ESElementary Stream containing Access Units
I,B,P
Timing DTS/PTS
Data
M U L T I P LEXER
System Time Clock (STC)
M O D U L A T O R
Encoder
Packetiser
ES
PES
Video
Packetiser
PES
Presentation Units
Data
Transport Stream
PES
Encoder
Packetiser
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
21
Creating a Transport Stream

• Compression of Presentation Units to yield Access
  Units. Succession of AUs comprises an Elementary
  Stream(ES)
• Packetisation of an elementary stream to yield a
  packetised elementary stream (PES).
• Distribution of PES packet content amongst a
  number of fixed size Transport Packets (size0 in
  ATSC)
• Add timing information to PES Transport Packets
• Add Programme Specific Information (PSI)
• Sequential output of transport packets forms an
  MPEG-2 Transport Stream with a constant bit rate
  (CBR)

22
Packetised Elementary Streams (PES)

• Contains Only Audio or Video or Data Access
  Units- no programme guide information
• Variable in size . Maximum 64Kbytes.
• Header may contain Timing Information-
• Decoder Time Stamp (DTS)
• i.e.. when to decode a Video AU
• and/or
• Presentation Time Stamp (PTS)
• i.e.. when to present to the viewer a decoded
  video or audio AU
• For audio PTS refers to first AU in packet.
• For video DTS/PTS refers to AU containing first
  picture start code commencing in packet.

23
PES Packet
24 bits
8 bits
16 bits
Packet Start Code Prefix
Stream Id
PES Packet length
Data Bytes
Optional PES Header
8 bits
2 bits
8 bits
PES scrambling control
PES Header Data length
Optional Fields
Stuffing Bytes
10
7 flags
2 bits
Optional Fields PES ext
PES CRC
ESCR
ES Rate
DTS
PTS
33 bits
33 bits
42 bits
22 bits
Optional Fields
5 flags
PES Private data
24
PES Packet

• For coding constraints set by ATSC on PES packet
  header and extension and video and audio PES
  constraints refer to A/53 Annex(C) section 5.5.
  Some of the constraints are as follows.
• PES_scrambling _control shall be coded as 00
• PES_packet _length shall be coded as 00
• data_alignment _indicator shall be coded as
  1.This is related to a constraint in the PSI. See
  section 5.4.
• value of stream_id for AC 3 shall be 1011
  1101(private_stream_1)

25
Transport Stream Packets
188 Byte Packet
4 Byte Packet Header
Adaptation Field (if present)
Payload (if present)

• 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

26
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

27
The Packet Header
28
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.

29
PSI Information-the table structure

• PID 0

Programme Association Table - PAT
NIT
PID 16
Network Information Table
Prog 0
PID16
Prog 1
PID 20
Prog 2
PID 30
PID20
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
30
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
31
PCR Value
PCRn PCR base PCR extension Tn PCR base /
90x103 PCR ext / 27x106 300x PCR base
/ 27x106 PCR Extension/ 27x106 The 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 106 Hz
Counter 233
PCR extension
PCR base
32
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

33
Overall Timing Jitter
Overall Jitter
PCR Inaccuracy
PCR Arrival Time Jitter


Clock Frequency
Counter error
Variable Network Delay
Clock drift
Re-multiplexing
34
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
35
What are PTS DTS?

• DTS is the Decode Time Stamp. It is a 33 bit
  data field indicating the appropriate time
  according to the STC that a particular AU should
  be decoded.
• PTS is the Presentation Time Stamp derived from
  the same clock as the DTS. It controls when a
  decoded access unit (ie a presentation unit) is
  presented to the viewer.
• It is no coincidence that the above timestamps
  are 33-bits wide. This is the same width as the
  PCR base in terms of which the STC can be
  expressed. Decoding and presentation take place
  when the decoder STC advances to the time
  specified by the DTS and the PTS respectively.
• Both timestamps are found in the PES header
  packet

36
Decoder Buffer(T-STD)

• hh

Decoder control via PTS/DTS
Video Data buffer
Video Decoder
Re-order buffer
MPEG 2 TS
System demux and extract PCR
STC Generator
STC
Decoder control via PTS/DTS
Audio Data buffer
Audio Decoder
37
T-STD Buffer model
TS Packets
38
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.

39
DTV in regions of the world

• DVB adopted in Europe and parts of Asia. Uses
  MPEG12 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)

40
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

41
DVB Overview
Testing VidTrans October 2002 Dennis Kucera
42
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

43
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

44
So, what more are the broadcasters asking for?
What does this mean?..
45
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.

46
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

47
TR101 290

• Baseband measurements split into 3 groups
• 1st priority
• 2nd priority
• 3rd priority

48
TR101 290 1st Priority
No Indicator 1.1 TS_sync_loss 1.2
Sync_byte_error 1.3 PAT_error 1.4 Continuity_c
ount_error 1.5 PMT_error 1.6 PID_error
49
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
50
TR 101 290 3rd Priority
No Indicator 3.1 NIT_error 3.2
SI_repetition_error 3.3 Buffer_error 3.4 Unref
erenced_PID_error 3.5 SDT_error 3.6 EIT_error 3.
7 RST_error 3.8 TDT_error 3.9 Empty_buffer_err
or 3.10 Data_delay_error
51
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)

52
PCR measurements

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

53
In-Service Monitoring

• Continuous monitoring for 24 hours a day, 365
  days a year
• Required by
• Broadcasters
• Regulators
• Service providers

54
In service monitoring system requirements

• Comprehensive real time monitoring
• Remote control
• Logging of faults
• Variety of interfaces
• Simplified User Interface

55
Monitoring parameters

• TR101 290 1st, 2nd and 3rd Priority
• Bit rate
• Templates