DVB Overview - Cascade Range

DVB Overview!
Introduction to MPEG-2 Compression
and Transport Streams
November 2002
Dennis Kucera
Tektronix, Inc.
1
The Digtal Video Broadcasting Initiative
4  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.
4  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.
4  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.
2
The European DVB Project
4  Set up to address:-
0 Transmission Standards
0 Modulation Systems
0 Error Correction
0 Integrated Receiver/Decoders (IRD)
0 Service Information
that were not covered by MPEG-2
4  Now adopted world-wide
4  See DVB V2.0 CD-ROM (www.DVB.org)
3
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
4
DTV Transmission Chain
ES=Elementary Stream
containing
Access
Units I,B,P
Video Encoder
Presentation
Units
Audio
Encoder
ES
Data
ES
???
Programme Specific
Information(PSI) or
Service Information
(SI)
Timing
DTS/PTS
Data
Packetiser
Packetiser
Packetiser
Packetiser
PES
PES
PES
PES
M
U
L
T
I
P
L
E
X
E
R
MPEG Compression Layer
MPEG Systems Layer+ DVB/ATSC/ARIB
Basic
Standards
5
13818-2 A/53 atsc
13818-3 A/52 ac3
13818-4
13818-1
13818-4
ETS 300-468 A65 PSIP
ETR 290
ETR154
A54
System
Time
Clock
(STC)
Transport
Stream
M
O
D
U
L
A
T
O
R
DVB
ATSC
ISDB
QPSK , OFDM
QAM HM
8VSB
The Standards
4  The MPEG-2 video compression standard and transport mechanism are
common to DVB, ATSC & ISDB.
4  Three audio compression standards are in use namely MPEG-1&2, Dolby
AC3 and AAC.
4  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.
6
MPEG-2 Core Standards
4  ISO/IEC 13818-1 (systems)
0 Transport Stream and PES syntax
0 T-STD Buffer model (decoder)
0 PSI definition (PAT,PMT, CAT,NIT)
0 Definition of PCRs, PTS and DTS
4  ISO/IEC 13818-2 (video coding)
0 Uses MPEG-1 as base syntax for Sequence, GOP, Picture, Slice
and Macro Block syntax
0 Five coding Profiles and four source formats or Levels
0 Coding on frame or field basis-interlace.
7
MPEG-2 Core standards
4  ISO/IEC 13818-3 (audio coding)
0 Builds upon ISO/IEC11172-3 (MPEG-1)
0 Defines extensions for Multichannel audio and lower sampling
frequencies
0 Very rare usage?
4  ISO/IEC 13818-6 (DSM-CC, 1996 addition to MPEG-2))
0 User-to-User functionality
0 User-to-Network functionality
0 Basis for Data Broadcast
8
Base Band Standards
4  TR 101 154 Systems Implementation guidelines
0 Coding and decoding
0 Minimum receiver functionality
0 Really an extension of 13818-1
9
Base Band Standards
4  ETS 300 468 SI specification
0 Defines the SI table mechanism
0 Defines the SI tables
0 Defines the descriptors
4  TR 101 211 SI Implementation guidelines
0 Defines rules of operation
4  TR 101 162 Allocation of SI codes for particular
broadcasters
10
Base Band Standards
4  EN 301 192 Specification for Data broadcasting
0 Defines 5 data broadcasting profiles (extractions from 13818-6)
4  TR 101 202 Implementation Guidelines for data
broadcasting
0 Rules of operation for data broadcasting
11
Base Band Standards
4  EN 500083-9 Interfaces for CATV/SMATV headends and
similar professional equipment
12
DVB Transmission Standards
4  Satellite
4  Cable:
4  Terrestial:
13
DVB-S
DVB-C
DVB-T
Test Standards
4  MPEG
0 ISO/IEC 13818-4 (conformance) Baseband only.
4  DVB
0  TR101 290 Baseband and Transmission Measurement
4  ATSC
0 A64 Transmission Measurement and Compliance.
14
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 .
4  For Terrestrial Broadcast and Cable A/65 replaces:
0 A/55 - Program Guide for Digital Television
0 A/56 - System Information for Digital Television
which remain valid for satellite.
4  A/90 - Data Broadcasting
4  A/91 - Implementation guidelines for data.
4 
4 
4 
4 
4 
4 
4 
4 
4 
4 
15
ISDB Standards
4  Satellite
0 ARIB STD-B20 System
0 SRIB STD-B21 Receivers
0 ARIB STD-B25 CA
0 ARIB STD-B10 Service Information
0 ARIB STD-B24 Data Coding
4  Terrestrial
0 To be drafted System
0 To be drafted Receivers
0 Other standards as for satellite.
4  Cable Draft
16
MPEG- 2 Formats
17
The 4:2:2 Profile
4  Intended for professional video applications where ease
of editing and multi generation coding /decoding of video
are important.
4  I pictures are necessary which also result in high coding
bit rates.
4  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  4:2:2 profile is compatible with the Main Profile.
4  Maximum bit rate = 50 Mbit/s (300 Mb/s for HD)
18
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.
19
DTV Transmission Chain
ES=Elementary Stream
containing
Access
Units I,B,P
Video Encoder
Presentation
Units
Audio
Encoder
ES
Data
ES
???
Programme Specific
Information(PSI) or
Service Information
(SI)
Timing
DTS/PTS
Data
Packetiser
Packetiser
Packetiser
Packetiser
PES
PES
PES
PES
M
U
L
T
I
P
L
E
X
E
R
MPEG Compression Layer
MPEG Systems Layer+ DVB/ATSC/ARIB
Basic
Standards
20
13818-2 A/53 atsc
13818-3 A/52 ac3
13818-4
13818-1
13818-4
ETS 300-468 A65 PSIP
ETR 290
ETR154
A54
System
Time
Clock
(STC)
Transport
Stream
M
O
D
U
L
A
T
O
R
DVB
ATSC
ISDB
QPSK , OFDM
QAM HM
8VSB
Creating a Transport Stream
0 Compression of Presentation Units to yield Access Units.
Succession of AUs comprises an Elementary Stream(ES)
0 Packetisation of an elementary stream to yield a packetised
elementary stream (PES).
0 Distribution of PES packet content amongst a number of
fixed size Transport Packets (size=0 in ATSC)
0 Add timing information to PES & Transport Packets
0 Add Programme Specific Information (PSI)
0 Sequential output of transport packets forms an MPEG-2
Transport Stream with a constant bit rate (CBR)
21
Packetised Elementary Streams (PES)
4  Contains Only Audio or Video or Data Access Units- no
programme guide information
4  Variable in size . Maximum 64Kbytes.
4  Header may contain Timing Information:-
0 Decoder Time Stamp (DTS)
4 i.e.. when to decode a Video AU
and/or
0 Presentation Time Stamp (PTS)
4 i.e.. when to present to the viewer a decoded video or audio
AU
4  For audio PTS refers to first AU in packet.
4  For video DTS/PTS refers to AU containing first picture start
code commencing in packet.
22
PES Packet
24 bits
Packet Start
Code Prefix
8 bits
16 bits
Stream
Id
PES Packet
length
Optional PES
Header
2 bits
PES scrambling
control
10
Data
Bytes
8 bits
8 bits
7 flags
PES Header
Data length
Optional
Fields
Stuffing
Bytes
2 bits
PTS
DTS
33 bits
33 bits
ESCR
42 bits
ES Rate
PES
CRC
22 bits
5 flags
PES Private
data
23
Optional
Fields PES
ext
Optional
Fields
PES Packet
4  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.
0 PES_scrambling _control shall be coded as 00
0 PES_packet _length shall be coded as 00
0 data_alignment _indicator shall be coded as 1.This is related to a
constraint in the PSI. See section 5.4.
0 value of stream_id for AC 3 shall be 1011 1101(private_stream_1)
24
Transport Stream Packets
188 Byte Packet
4 Byte
Packet
Header
Adaptation Field
(if present)
Payload
(if present)
4  Fixed length of 188 bytes
4  Packets contain one type of data only i.e video,audio,
data, programme guide information.
4  May also carry timing information (PCR)
4  Every 4 Byte Header Contains following fields:
0 sync byte 0x47
0 transport error indicator
0 payload unit start indicator
25
Transport Packets
0 Transport priority
0 PID
0 Scrambling Control
0 Adaptation field control
0 Continuity Counter.
4  Adaptation field used either for stuffing or for
information. This is only stuffing method allowed for
transport packets carrying PES packets.
4  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.
4  Null Packets
26
The Packet Header
27
Programme Guide Information
4  PSI - Programme Service Information. This is defined by MPEG and
consists of
PAT,PMT,CAT,NIT,TSDT
4  SI - Service information. These are additional tables defined by DVB
(eg SDT,TDT,EIT etc)
(two categories Mandatory & optional)
4  PSIP - Additional tables defined by ATSC for terrestrial and cable
only (MGT,VCT etc)
4  ARIB SI- Additional tables defined by ARIB in Japan for satellite.
28
PSI Information-the table structure
PID 0
Programme Association Table - PAT
NIT
PID 16
PID20
Prog 0
PID16
Prog 1
PID 20
Prog 2
PID 30
Network
Information Table
PID 30
Programme Map table
PMT
PID No.
Transport Packets
29
Stream
Type
PID
Stream
Type
PID
1
Video
19
1
Video
50
2
Audio
33
2
Audio
42
3
Audio
29
3
Audio
35
20
30
0
PAT
Prog 1 Prog 2
PMT PMT
19
Prog1
Vid1
35
Prog2
Audio2
33
Prog1
Audio1
50
Prog2
Vid1
42
Prog2
Audio1
Prog 1
Audio2
Programme Map
table PMT
Program Clock Reference (PCR)
4  What it does
0 Enable the MPEG decoder to
synchronise to the encoder.
4  How it does it
0 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.
0 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.
30
System
Time
Clock
(STC)!
PCR
PCR Value
PCRn =PCR base + PCR extension!
Tn = PCR base / 90x103 + PCR ext / 27x106!
= 300x PCR base / 27x106 + PCR Extension/ 27x106 90x103 Hz!
Modulo 300!
27x 106 Hz!
The PCR value displayed by Adherent represents the number of cycles of the 27Mhz
clock each of duration 37nSec.!
i.e. clock ʻticksʼ!
PCR
extension!
Counter!
233!
PCR base!
31
PCR Tolerances
4  Decoders use PCRs to generate video timing And
sometimes colour burst . Therefore there are strict
limits on PCR repetition rate, accuracy .
4  The recommended repetition rate is between
40-100ms
4  PCR inaccuracy must be less than +/- 500 nS
32
Overall Timing Jitter
33
The PLL
PCR1
PCR2
PCR3
34
Encoder
Encoder STC
0 sec
.1 sec
.2 sec
Path Delay
1sec
Decoder
Enc. STC
1 sec
1.1 sec
1.2 sec
Dec. STC
0 sec
.1 sec
.2 sec
What are PTS & DTS?
4  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.
4  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.
4  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.
4  Both timestamps are found in the PES header packet
35
Decoder Buffer(T-STD)
4 
hh
Video
Decoder
control
Data
buffer
Video
Decoder
via
PTS/DTS
MPEG 2
TS
Re-order
buffer
System demux
and
STC
Generator
extract PCR
Audio
Data
buffer
36
STC
Decoder
control
via
PTS/DTS
Audio
Decoder
T-STD Buffer model
Delay
Access Units
Video TS Packets
Transport Buffer
Multiplex Buffer
Elementary
Decoder
Buffer
Video Decoder
Decoded
Presentation Units
TS Packets
Transport Buffer
Transport
Buffer sys
37
Elementary
Decoder
Buffer
Elementary
Decoder
Buffer sys
Access Units
Decoder
Decoded
Presentation Units
System data
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.
38
DTV in regions of the world
4  DVB adopted in Europe and parts of Asia. Uses
MPEG1&2 or Dolby AC3 audio.
4  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.
4  Japanese ISDB followed on with similar aspirations
but with HDTV and standard definition in one system.
Uses MPEG AAC advanced audio coding (like MPEG4)
39
Audio compression systems used
in MPEG-2 transport streams
4  MPEG-1 layers 1, 2 & 3 (Europe & DVB domain)
4  layer-II used in broadcast systems
4  MPEG-2 audio (5.1 channels) possible, but rarely used
4  All are ‘backwards compatible’
4  Dolby digital (AC3) USA ATSC and also DVB (Germany)
4  5.1 channels (0.1 = low freq effects)
4  AAC (Japan) ADIFF and ADTS type audio
4  MPEG-4 will use AACas default standard
(Frauhoffer labs) 8 or more channels dynamically reposition-able
in space
40
DVB Overview!
Testing
VidTrans
October 2002
Dennis Kucera
41
Types of Errors
Priority
4  Errors that prevent decodability
1
4  Errors which impair decodability
2
0 artifacts in the decoded picture
0 intermittent decoding
4  Errors that indicate a problem
at the encoder or multiplexer
but do not affect decodability
42
3
Test Documents
4  MPEG
0 13818-4-MPEG
0 Covers all layers ES to TS
4  DVB
0 13818-4 and
0 TR101 290-DVB
4 Covers Systems Layer only + RF
4 Refers to 13818-1, TR101 211, ETS 300,468 and others.
4  ATSC
0 13818-4
0 A54,A65
43
So, what more are the broadcasters
asking for?
What does this mean?…..
44
Templates- definition
4  A Template profile consists of a unique combination of tests,
defined by a user, depending on his particular custom
monitoring needs.
4  The tests forming the part of a template profile can
encompass standard tests [TR101290] and proprietary tests.
4  Each ‘template applied’ test can have maximum, minimum or
‘window’ parameter range associated with it.
45
Template Profile example
Template Profile 1
Network ID:
Transport Stream ID: 16640
Service Ids
 
 
 
4164
9018
(0x4100)
(0x233A)
Monrovia News-48
  PIDS
  101
  102
  105
 
4228
Video with PCR
Audio
DVB Subtitle
Widgets Interactive channel
  PIDs
  610
  611
  720
46
Video with PCR
Audio
DSMCC object carousel
TR101 290
4  Baseband measurements split into 3
groups
0  1st priority
0  2nd priority
0  3rd priority
47
TR101 290 1st Priority
48
No:
Indicator
1.1
1.2
1.3
1.4
1.5
1.6
TS_sync_loss
Sync_byte_error
PAT_error
Continuity_count_error
PMT_error
PID_error
TR 101 290 2nd Priority
49
No:
Indicator
2.1
2.2
2.3
2.4
2.5
2.6
Transport_error
CRC_error
PCR_error
PCR_accuracy_error
PTS_error
CAT_error
TR 101 290 3rd Priority
50
No:
Indicator
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
3.10
NIT_error
SI_repetition_error
Buffer_error
Unreferenced_PID_error
SDT_error
EIT_error
RST_error
TDT_error
Empty_buffer_error
Data_delay_error
PSI - PAT, PMT tests
4  For the PAT TR 101 290 specifies
0 Repetition rate of PID 0 less than 0.5s
0 Scrambling control set to 00 (unscrambled)
0 PID 0 must contain only PAT sections
4  For a PMT TR 101 290 specifies
0 Repetition rate less than 0.5s
0 Scrambling control set to 00 (unscrambled)
51
PCR measurements
4  TR101 290 measurements
0 PCR_error
4 Discontinuity of > 100 ms
4 Repetition rate
0 PCR_accuracy_error
4 Accuracy of encoded PCR values
52
In-Service Monitoring
4  Continuous monitoring for 24 hours a day, 365 days a
year
4  Required by:
0 Broadcasters
0 Regulators
0 Service providers
53
In service monitoring system requirements
4  Comprehensive real time monitoring
4  Remote control
4  Logging of faults
4  Variety of interfaces
4  Simplified User Interface
54
Monitoring parameters
4  TR101 290 1st, 2nd and 3rd Priority
4  Bit rate
4  Templates
55