mpeg 101 demyst analysis & picture symptoms 20110808 opt

MPEG 101 MPEG 101 ––Transport Stream Demystification Transport Stream Demystification by Leon Urban, Sr. Sales Engineerby Leon Urban, Sr. Sales EngineerAugust 17, 2011 San Juan, PR for CCTA membersAugust 17, 2011 San Juan, PR for CCTA membersAugust 17, 2011 San Juan, PR for CCTA members August 17, 2011 San Juan, PR for CCTA members

In collaboration with our Caribbean Value Added Reseller:

An LG Electronics CompanyMario Sebastiani & Bernard How

Basic MPEG Building BlocksBasic MPEG Building Blocks

An LG Electronics Company

Typical DTV Transport StreamTypical DTV Transport Stream

Special case of MPEG-2 transport stream May contain multiple virtual channels Video channels A video stream

One or more audio streamsOne or more audio streams

Possibly one or more data streams

Audio channels One or more audio streams

Possibly one or more data streams

Data only channels Data-only channels One or more data streams

An LG Electronics Company Copyright © 2009 Triveni Digital, Inc.

MPEGMPEG--2 Transport Stream2 Transport Stream

Made up of 188-byte transport packets, each with 4 byte header & 184 byte payload

E h k t t i ONE ki d f i f ti Each packet contains any ONE kind of information–audio, video, data, PSI, …

One One Transport (MPEG) Packet

Transport (MPEG) Packet


MPEGMPEG--2 Transport Stream (Contd.)2 Transport Stream (Contd.)

We say transport packets have multiple interleaved elementary streams -- audio, video, data, PSI, ...

P k t b l i t th l t t Packets belonging to the same elementary stream are identified by packet id (PID) in packet header (same color in our illustrations). )

MPEG-2 Transport Stream

These three packets are the same color. They have the same PID and belong to the same Elementary stream


the same Elementary stream.

MPEGMPEG--2 Transport Stream 2 Transport Stream –– Header FieldsHeader Fields

Noteworthy fields:

1) Sync Byte – Find packet boundary

2) PID – Used while demultiplexing stream

3) Continuity Counter – Identify packet loss

4) PCR stamp in adaptation field – Clock sync

188 BytesHeader (4 Bytes)


AdaptationField

ContinuityCounter

SyncByte PID

188 Bytes

PES 1Adaptation

Field(Optional)

PIDSyncByte

ContinuityCounter PES x Or other Payload (Pat, PMT, PSIP,

etc)……………………………...


MPEG Header Fields: Sync ByteMPEG Header Fields: Sync Byte

When a decoder first tunes, all it sees are a stream of 0’s and 1’s

Th d d t fi t id tif th b i i f The decoder must first identify the beginning of packets before it can interpret the stream

The decoder uses the Sync Byte field to do thisThe decoder uses the Sync Byte field to do this

01010001111010010101101010001100011110010111000

MPEG Data Prior to Packet Sync


MPEG Header Fields: Sync Byte (Contd.)MPEG Header Fields: Sync Byte (Contd.)

The Sync Byte of a packet is always 0x47 (Hexadecimal) or 01000111 binary

The decoder looks for strings of zeros and ones which match the pattern of the sync byte (see red below)

010100011101000111101001010110101000010001110100011111000111



Once the decoder finds a 0x47 in the stream, it looks 187 bytes down the stream, and looks for another 0x47

If it finds three Sync Bytes in a row, then the Decoder has Found y y ,Sync and assumes packet boundaries from then on

Each packet is tested for 0x47 as soon as it arrives. If a packet arrives with an incorrect sync byte the decoder starts over Thisarrives with an incorrect sync byte, the decoder starts over. This is called SYNC LOSS

Found Sync

0x470x47 187 bytes187 bytes 0x470x47 187 bytes187 bytes 0x470x47 187 bytes187 bytes Packet 188 bytesPacket 188 bytes0x47 187 bytes 0x47 187 bytes 0x47 187 bytes Packet 188 bytes

Sync Not Found

0x320x32 1101010101011101101010101000111010101010111011010101010001Packet 188 bytesPacket 188 bytes Packet 188 bytesPacket 188 bytes 0x32 11010101010111011010101010001Packet 188 bytes Packet 188 bytes



If you don’t have Packet Sync, the decoder cannot find packet boundaries. You will not be able to decode at allall

Packet Sync problems typically occur in hardware at packet boundaries during format converters, edge g gdevices, demodulators etc: ASI to Gig-E

ASI to Microwave or QAM

Satellite to ASI


PIDs Defined PIDs Defined -- ATSC BitstreamATSC Bitstream

PSIP Tables PATPAT

PMTPMT

VideoVideo

AudioAudio

DataData

PAT

PMT

Video

Audio

Data

PSIP Generator

Data channel

Data-

NullNullDataData

PSIPPSIPNull

Data

PSIPData Server

Data ServerM lti

Video Encoder

Audio Encoderenhanced Audio/Video

channel

Multi-plexer

Audio Encoder

Video Encoder

Audio/Video channel



PIDs Defined PIDs Defined -- Digital Cable BitstreamDigital Cable BitstreamA di E d PAT

PMT

Null

VideoAudio

Video Encoder

Audio EncoderVideo/Audio channel Video

AudioVid

Video/Audio channel

CAT

Video Encoder

Audio Encoder

M lti

VideoAudio

VideoAudio

Video Encoder

Audio EncoderVideo/Audio channel

Multi-plexer

Audio Encoder

Video Encoder

Video/Audio channel



MPEGMPEG--2 PSI Tables (Contd.)2 PSI Tables (Contd.)

Decoder: Receiver or Set top Box

“WXXX Channel Video”PID 0x31 Program 1

“WXXX Channel Audio”PID 0x34 Program 1

PSI via PID assignments and descriptors tells the decoder that these PIDS go together to make up a program


g p p g

Transport Stream DemultiplexingTransport Stream Demultiplexing

When a set top box first receives a Transport Stream, it demultiplexes that stream based on PID

Decoder: Receiver or set top box

Program 01 Vid

Program Program Program 01 A di

Program 02 Audio Program

03 AudioPSIP

PAT/PMT/MPEG T bl


01 Video 02 Video 03 Video 01 Audio 03 AudioTablesTables

MetadataMetadata

Data about included data is metadata

Metadata tells the decoder which kinds of informationMetadata tells the decoder which kinds of information are contained in each PID, and which PID’s go together.

There are two kinds of Metadata

Program Specific Information (PSI) - Tables in the stream defined in the MPEG standards

Program and System Information Protocol (PSIP) -Tables defined in ATSC A/65Tables defined in ATSC A/65


MPEG 101 Knowledge Check #1MPEG 101 Knowledge Check #1

Q:Q: How How manymany of of whatwhat must the decoder must the decoder QQ yysee before it can begin decoding a digital see before it can begin decoding a digital

video stream ?video stream ?


PSI Data In the StreamPSI Data In the Stream


PSI Tables (MPEGPSI Tables (MPEG--2 Tables)2 Tables)

PAT - Program Association Table Appears in PID 0x0000pp

Identifies MPEG-2 programs in transport stream and gives PIDs for their PMTs

Th PAT i PID 0 00 Thi i th fi t PID ‘B PID’ The PAT is on PID 0x00. This is the first PID or ‘Base PID’ a MPEG decoder looks for

bl PMT - Program Map TableIdentifies elementary streams in program (virtual channel), and gives their PIDs. ), g



PMT 1Video PID 0x31Audio PID 0x34Audio PID 0x35 PCR_PID 0x31

PMT 2Video PID 0x41Audio PID 0x44Audio PID 0x45PCR PID 0x41

PAT (always on PID 0x0)

Station TSID

PMT 1 -> On PID 0x30PMT 2 > On PID 0x40

PID 0x40

PCR_PID 0x41

PMT 3Video PID 0x51Audio PID 0x54

PMT 2 -> On PID 0x40PMT 3 -> On PID 0x50

Audio PID 0x54Audio PID 0x55PCR_PID 0x51


Graphical View of PAT/PMTGraphical View of PAT/PMT

Elementary streamsfound in this PMT

Elementary streamsfound in this PMT

Descriptor Defines

Additional Stream

Characteristics

(PID 0x0000)Program 2

PID for PMT

Program 3PID for

found in this PMT


PMT PID for PMT

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Decoder: Receiver or Set top Box

“WXXX Channel Video”PID 0x31

“WXXX Channel Audio”PID 0x34

PSIPID assignments

Th PIDS t th


These PIDS go together

PSIP Data In the StreamPSIP Data In the Stream


PSIP BackgroundPSIP Background

Program and System Information Protocol

Metadata inserted into broadcast stream

Enables: Tuning to virtual channels

Displaying channel name (on channel changes)

Interactive electronic program guides (EPGs)

Automatic language selection for audio trackAutomatic language selection for audio track

Caption decoding

“V-Chip” function (parental content blocking)p (p g)

Accurate receiver time-of-day clock setting

Redistribution Control


Basic functions of PSIP Tables Basic functions of PSIP Tables

BrandingBranding – Station call letters and channel numbergg

SignalingSignaling V Chip data information about audio andSignalingSignaling – V-Chip data, information about audio and Video PID’s, Virtual Channel Table

AnnouncementAnnouncement – Electronic Program Guide (EPG)


Signaling vs AnnouncementSignaling vs Announcement

SignalingSignaling Information about what is "on now" Used to assemble program elements into whole

Provides linkages Ex: PMT and/or VCT used to link different components of television

program (i.e. video and audio)

Used to define characteristics of current program (descriptors0 Captioning, ratings, redistribution…

AnnouncementAnnouncement Information about what will be available in the future Program Guide information (name, description schedule) Characteristics of future programs (captioning, ratings,Characteristics of future programs (captioning, ratings,

redistribution…) Typically does not provide linkages between program elements


PSIP Generation ArchitecturePSIP Generation Architecture

Encoder(s)Traffic/Program

SystemTraffic/Program

SystemTraffic/Program

System

PSIP PSIP PSIP MU

TimeTimeTime

Remote Remote Remote GeneratorGeneratorGenerator U

XAutomation System

Automation System

Automation System

e oteGUI(s)e ote

GUI(s)e ote

GUI(s)

Listing Listing Listing Staging Staging Staging

FIREg

Serviceg

Serviceg

Service ServerServerServerEWALL


PSIP metadata found in the ‘Payload’PSIP metadata found in the ‘Payload’

Noteworthy fields:

Payload contains PSIP, PAT, PMT metadata

H d (4 B t )

MPEG-2 Transport StreamPSIP

metadatafound in the

packet ‘Payload’

AdaptationField

ContinuityCounter

SyncByte PID


PES 1Adaptation

Field(Optional)

PIDSyncByte


etc)……………………………...

Payload


ATSC PSIP TablesATSC PSIP Tables

MGT - Master Guide Table Interval: 150msInterval: 150ms- Appears in PID 0x1FFB.- Gives PIDs, sizes, and version numbers of other PSIPGives PIDs, sizes, and version numbers of other PSIP tables (except STT). A directory of all PSIP tables.

STT S t Ti T bl I t l 1 000 (1 )I t l 1 000 (1 ) STT - System Time Table Interval: 1,000ms (1 sec)Interval: 1,000ms (1 sec)- Appears in PID 0x1FFB- Gives current UTC time.

VCT - Virtual Channel Table Interval: 400msInterval: 400ms- Identifies and describes virtual channels- Identifies and describes virtual channels.


ATSC PSIP Tables (Contd.)ATSC PSIP Tables (Contd.)

RRT- Rating Region Table Interval: 60,000ms (1 min)Interval: 60,000ms (1 min)- Describes content advisory system(s) being used to rate events.events.

EIT - Event Information Table

EIT has variable intervals:EIT has variable intervals:EITEIT--0: 500ms0: 500msEITEIT--1: 3,000ms1: 3,000msEITEIT--2 & up: 60,000ms2 & up: 60,000ms

- Gives titles, start times, durations, content advisory ratings of events (TV programs).

p ,p ,

ETT - Extended Text Table Interval: Follows it’s EITInterval: Follows it’s EIT- Gives extended textual descriptions of virtual channels and events.


PIDs in the StreamPIDs in the Stream

PAT points to PMT

PAT points

toPMT

PSIPPSIP metadata

tables: VCT, MGT, STT,

EITs & ETTs


Details of FCC R&O Details of FCC R&O –– PSIP relatedPSIP related

"…fully implement PSIP to the extent that ATSC A/65B requires." Required transmission of all mandatory tables and descriptorsRequired transmission of all mandatory tables and descriptors MGT, TVCT, EIT-03, STT, RRT (except region 1)

Required tables and descriptors must be populated ith d t i f tiwith proper and correct information

At least 12 hours of populated EITs (EIT-0 thru 3) EITs must contain correct schedule informationEITs must contain correct schedule information Each EIT contains 3 hours worth of event information

Major channel rules from PSIP (A/65B) adoptedj ( / ) p Correct Major Channel number must be used Correct TSIDs (Transport Stream ID) must be used


VCT VCT ---- Virtual Channel Concept Virtual Channel Concept

Breaks the link between RF channel number and user’s notion of channel number Analog broadcast “channel number” was the same as the

RF carrier designation

Digital broadcast “channel number” is defined by VirtualDigital broadcast channel number is defined by Virtual Channel Table (VCT)

One digital TS can include multiple channels of iprogramming

8-VSB carrier freq. may have (probably) shifted during transition (June 2009)transition (June 2009)


VCT: Two Part Channel NumbersVCT: Two Part Channel Numbers

1st part: “major channel” (Original analog channel)

2nd part: “minor channel”

Broadcasters retain their brand identity Digital services groupable with analog

KZZZ has been associated with Channel 7 for years; KZZZ-DT can be found on Channel 7-1


Virtual Channel Table (VCT)Virtual Channel Table (VCT)

Has same info as PAT & PMTs, plus more.

Allows tuning by virtual major-minor channel number, th th h i l h l b d MPEG 2rather than physical channel number and MPEG-2

“program” number.

Allows language track selectionAllows language track selection.

Allows channel name to be displayed on channel changes and in EPG. g

ATSC receivers are designed to use VCT; may have trouble with PAT and PMTs alone.


Comparing PAT vs. VCTComparing PAT vs. VCTPAT (P A i ti T bl ) VCT (Vi t al Channel Table)PAT (Program Association Table)Table IDSection Syntax IndicatorSection LengthTransport Stream ID (TSID)

VCT (Virtual Channel Table)Table IDSection Syntax IndicatorSection LengthTransport Stream ID (TSID)p ( )

Version NumberCurrent Next IndicatorSection NumberLast Section NumberProgram Number

p ( )Version NumberCurrent Next IndicatorSection NumberLast Section NumberATSC protocol versionProgram Number

Program Map PIDATSC protocol versionNumber of Channels in SectionShort NameMajor Channel NumberMinor Channel NumberModulation ModeChannel TSIDProgram NumberExtended Text Message LocationDescriptor LengthDescriptor LengthDescriptor ( )Source IDService TypeAccess ControlledHidd / Hid G id


Hidden / Hide Guide

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Virtual Channel Table (VCT)Virtual Channel Table (VCT)

Virtual ChannelSh t Ch l N• Short Channel Name

• Major Channel Number• Minor Channel Number• Modulation Mode

F• Frequency• TS ID (of Virtual Channel)• Program Number (in Stream)• Extended Text Location

A C t ll d ?• Access Controlled ?• Hidden ? Hide from Guide?• Service Type (A/V/D)• Source ID

S i L ti D

Video Stream

Eng Audio Stream• Service Location Descr• other descriptors Fre Audio Stream(PID 0x1FFB)


PSIP and PSI LinkPSIP and PSI Link

Table Information for aTelevision Broadcast Stream

PMT 1(On PID 0x30)Video PID 0x31Audio PID 0x34

PAT (On PID 0x0)

Station TSID

VCT On Pid 0x1FFB4-1WXXXAudio PID 0x34

PCR_PID 0x31PMT 1 -> On PID 0x30WXXXVideo PID 0x31Audio PID 0x34

PAT and PMT Tables PSIP table


Continuity CounterContinuity Counter



Q: Name two tables found in PSI Q: Name two tables found in PSI metadatametadatametadatametadata


MPEG Header: Continuity CounterMPEG Header: Continuity Counter

The continuity counter is a 4 bit field in the header which increments by 1 each time a packet comes out on a specific PID:on a specific PID:

0 1 2 3 4 5 6 7 8 14 15 0 1……

All Packets PID 0x52

When a PID ‘skips’ one value of the continuity Counter, we call it a ‘Continuity Error.’ This means one or more packets were lost.

All Packets PID 0x54

Continuity Error Here

0 1 2 3 7 8 9 10 11 ……


MPEG Header: Continuity Counter (Contd.)MPEG Header: Continuity Counter (Contd.)

Identifies WHEN we lose Packets, but not HOW MANY!

Packet loss causes many other kinds of analysis to ‘reset’ or give bogus results.

Any analysis based on an average over many packets will automatically reset when it encounters continuity problems.

Since a continuity error mean ‘some packets’ have been lost,Since a continuity error mean some packets have been lost, frequent continuity errors should be one of the FIRST things you look for when debugging.


Three Things to RememberThree Things to Remember

Three main monitoring and troubleshooting lessons: Fix Continuity Problems first C ti it t b l i th Continuity errors create bogus alarms in other areas.

Until you resolve the continuity problems, it will be very hard to determine if you have other problems in your stream

To Be Discussed

To Be Discussed



Q: If the continuity counter on aQ: If the continuity counter on aQ: If the continuity counter on a Q: If the continuity counter on a given PID changes from 3 to 7, how given PID changes from 3 to 7, how

many packets have been lost?many packets have been lost?many packets have been lost?many packets have been lost?


Elementary streams:Elementary streams:yyEncoding Video & Audio Encoding Video & Audio DataDataDataData


MPEGMPEG--2 / MPEG2 / MPEG--4 Video Compression4 Video Compression

Digital Compression starts at the MPEG encoder

MPEG2 or MPEG4 CODECS can be carried in an MPEG2 Transport Stream

The encoder filters noise in the input signal and:

compresses baseband video & audio OR

uncompressed digitized video/audio/data (SDI)

Video and Audio elements are encoded into a sequence of frames

A frame is a single image from a video or audio sequence

In most countries, one frame occurs every 33 milliseconds, y

Each frame is encoded in one of three ways:


MPEGMPEG--2 Video/Audio Encoding2 Video/Audio Encoding

I Frames

I-picture: intra-picture encoding, similar to jpeg encoding (exploiting spatial redundancy).

Compressed solely on information found in the frame

Highest amount of data of all other frame types

‘Group Of Pictures’ always start with an I frameGroup Of Pictures always start with an I frame

B & P frames are calculated from the I frame

“I” stands for “Intra” coded

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B Frames

B-picture: bi-directional encoding, using motion adjusted deltas from a previous and a future frame (exploiting temporal redundancy)redundancy).

Uses Data from preceding and following I & P frames

Depends on data before and/or after in video sequencep d o da a b o a d/o a d o qu

Cannot calculate from another B frame



P Frames

P-picture: predictive encoding, using motion adjusted deltas from a previous reference frame (exploiting temporal p ( p g predundancy).

Compressed using data from closest preceding I or P frame

GOP ith b k t b k P f ll i di t f t ti GOP with back-to-back P frames usually indicate fast motion



Encoder emits sequence of encoded frames

Sizes of encoded frames vary y

Encoded frames are packed into packetized elementary stream (PES) packets.

PES packets are packed into MPEG-2 transport packets (All packets for single video stream have same PIDvalue)value)

Overall compression ratio is 50:1 or more

Cl d ti i i t d ith id f i Closed captioning associated with video frame is encoded here


MPEG-2 Elementary Stream

PTS DTS

PES PacketPayload

PESHeader

PES PacketPayload

PESHeader

PES PacketPayload

PESHeader

Only PTS on Audio PESpacket

MPEG-2 Elementary Stream

Payload PayloadPayload

AdaptationField

ContinuityCounter

SyncByte PID


PES 1Adaptation

Field(Optional)

PIDSyncByte


etc)……………………………...

OptionalFieldsLength Flags Stuffing

BytesAdaptation Field on Video

PID’s Only

PCR



Group of Pictures = GOP

Series of frames consisting of a single ‘I’ frame with P & B frames

A GOP begins with an ‘I’ frame and ends with last frame before the gnext ‘I’ frame

All frames within the GOP depend directly or indirectly on data from the I framethe I frame

Relationships between GOPs: Either OPEN or CLOSED

Closed GOP is self-contained. No dependance on data outside GOP

Open GOP can use data from I frame of following GOP


MPEGMPEG--2 Video/Audio Encoding (Contd.)2 Video/Audio Encoding (Contd.)

Example 1. Panning CameraI-picture B-picture I-picture

Example 2. Moving ObjectExample 2. Moving ObjectB-picture I-pictureI-picture



T i l GOP STypical GOP StructuresP Frame83.45 Kb

I Frame216.6 Kb

B Frame49 9 Kb

P P P P P PII B B B B B B B B B B B B BB B B

49.9 Kb

P P P P P PII B B B B B B B B B B B B BB B B

Typical low motion GOP sequence

I FrameP Frame44.5 Kb

I Frame183.2 Kb

P Frame59.9 Kb

P P P P P PIP P P P P P P P P P P P P PP P P

Typical high motion GOP sequence


ATSC/SCTE Audio FormatsATSC/SCTE Audio Formats

ATSC uses AC-3 audio encoding, with up to 6 audio channels: left, right, center, left surround, right surround, low frequency enhancement.surround, low frequency enhancement.

The full set is often called 5.1 audio.

The sampling rate is always 48 kHzThe sampling rate is always 48 kHz.

The encoded bit rate may be up to 384 kbps.


ACAC--3 Audio Encoding3 Audio Encoding

Audio frames, each 32 milliseconds in length, are encoded.

E d d f i d d l bit t Encoded frame size depends only on bitrate.

Encoded frames are packed into packetized elementary stream (PES) packetselementary stream (PES) packets.

PES packets are packed into MPEG-2 transport packets. (All packets for single audio stream have same PID ( p gvalue.)



Q: In MPEGQ: In MPEG--2 video encoding, what2 video encoding, whatQ: In MPEGQ: In MPEG 2 video encoding, what 2 video encoding, what are the three video frame types are the three video frame types

called?called?called?called?


Video and Audio Video and Audio deo a d ud odeo a d ud oSyncronization using Syncronization using PCRPCRPCRPCR


AudioAudio--Video SynchronizationVideo Synchronization

Audio, video are encoded independently, must be , p y,synchronized during play

MPEG has to allow for great distances AND network processing between the Encoder and Decoder and still allow for Correct Decode of the transport streamallow for Correct Decode of the transport stream


How to Assure Audio/Video Sync?How to Assure Audio/Video Sync?

In order for the audio and video Elementary Streams to remain in Sync the Encoder Clock and the Decoderremain in Sync, the Encoder Clock and the DecoderClock must remain in sync

The next few slides will demonstrate how this happensThe next few slides will demonstrate how this happens and what components to check when it fails…


Encoder Inserts PCR Encoder Inserts PCR

When the encoder streams creates packets, it embeds the current value of it’s 27 MHz clock into the stream

Thi ti f i ll d th PCR P Cl k This time reference is called the PCR: Program Clock Reference

MPEG demands that one PCR packet appear in theMPEG demands that one PCR packet appear in the stream every 100ms

Encoder27Mhz Clock

MPEG Packets

MPEG Packet with PCR Stamp


The Encoder and Decoder ClockThe Encoder and Decoder Clock

The MPEG encoder and MPEG decoder use a 27Mhz ‘clock’ to encode/decode incoming audio and video

Th l k i t ll ‘ t ’ hi h d The clock is actually a ‘counter’ which advances every 1/27000000 seconds

Encoder

27Mhz Clock

Encoder

27Mhz Clock

Encoder

27Mhz Clock

Decoder

27Mhz Clock

Decoder

27Mhz Clock

Decoder

27Mhz Clock

1 2 3 41 2 3 41 2 3 41,2,3,4…..1,2,3,4…..1,2,3,4….. 1,2,3,4…..1,2,3,4…..1,2,3,4…..


The Encoder and Decoder ClockThe Encoder and Decoder Clock

The MPEG encoder and MPEG decoder use a 27Mhz ‘clock’ to encode/decode incoming audio and video

Th l k i t ll ‘ t ’ hi h d The clock is actually a ‘counter’ which advances every 1/27000000 seconds

Encoder

27Mhz Clock

Encoder

27Mhz Clock

Encoder

27Mhz Clock

Decoder

27Mhz Clock

Decoder

27Mhz Clock

Decoder

27Mhz ClockMassive

1 2 3 41 2 3 41 2 3 4

NetworkProcessing

1,2,3,4…..1,2,3,4…..1,2,3,4….. 1,2,3,4…..1,2,3,4…..1,2,3,4…..


PCR Timestamp IssuePCR Timestamp Issue

What could conceptually cause PCR timestamp issues?

E d ibl i d i l Encoder possibly time stamped incorrectly

Decoder possibly failed to consume time stampsDecoder possibly failed to consume time stamps

PCR packet was accidentally lost in transmission

When PCR time stamps go awry, we have “PCR jitter”p g y, j


PCR Jitter DefinedPCR Jitter Defined

PCR Jitter is:

Difference between

the Actual Value of the PCR time stamped by encoderencoder

and

th E t d V l f th PCR l l t d bthe Expected Value of the PCR as calculated by decoder based on the clock rate and the time at which the PCR value is receivedat which the PCR value is received.

PCR Jitter spec: 500ns


PCR Rate (Frequency) OffsetPCR Rate (Frequency) Offset

PCR Frequency Offset is:

Difference between

the clock frequency calculated at decoder based on actual PCR values receivedbased on actual PCR values received

and

“id l” 27 MH l k hi h i th l k tan “ideal” 27 MHz clock, which is the clock rate dictated by the MPEG-2 standard

PCR Frequency Offset Spec: +/- 810 Hz


PCR Intervals, Jitter and RatePCR Intervals, Jitter and Rate

PCR spec summary:

Transmit interval: 100 ms

Jitter: no more than 500 ns

Rate: 27 MHz +/- 810 Hz

Most streams seen in the field are compliant, but every o a d a o p a , bu ynow and then extreme jitter shows up.

Here’s Why


PCR Packet Spacing PCR Packet Spacing BeforeBefore MuxingMuxing

Note the Number of Packets between each PCR packet in each Input Stream

Video 0x31

PID PacketVideo 0x41

PID Packet Spacing

0x31 2 Packets

TransportStreamMUX

Video 0x510x41 1 Packet

0x51 0 Packets

MUX


PCR Packet Spacing PCR Packet Spacing AfterAfter MuxingMuxing

Note that the PCR packet spacing has changed!

Video 0x31Video 0x31

PID Old Spacing New Spacing

Video 0x41 TransportStreamMUX

PID Old Spacing New Spacing

0x31 2 Packets 8 Packets

0x41 1 Packet 5 Packets

Video 0x51

0x51 0 Packets 2 Packets


Muxing Causes PCR JitterMuxing Causes PCR Jitter

When we MUX multiple streams together, the spacing between the PCR packets in each stream CHANGESstream CHANGES

The physical shift results in a TEMPORAL shiftThe physical shift results in a TEMPORAL shift as well, throwing the time stamps off

The TEMPORAL shift in PCR values is referred to as “PCR jitter”


Muxing Causes PCR Jitter (Contd.)Muxing Causes PCR Jitter (Contd.)

The MUX has to RESTAMP all the PCR values to correct for the change in the packet spacing – THIS IS VERY HARD TO DOspacing THIS IS VERY HARD TO DO

The more services on the output, the harder it is to restamp

The fewer ‘null’ packets at the output the harder it The fewer null packets at the output, the harder it is to restamp


PCR Timestamp Issue (Contd.)PCR Timestamp Issue (Contd.)

What in your network facility could cause PCR timestamp issues?

Th f th t Three of the most common are:

It can happen any time you MUX streamsIt can happen any time you MUX streams

It can happen at the source encodingpp g

It can happen on any IP link – due to network lag


PCR Jitter From Incorrect EncodingPCR Jitter From Incorrect Encoding

If the MPEG encoder’s parameters are set up incorrectly, you can introduce jitter at the source

Thi i l ti l h This is relatively rare, however If a national programmer sent it’s stream up to the bird with

jitter in it, the result would effect all receive sites !j ,

Re-encoded streams at the headend may also create PCR jitter

Local broadcast streams could create PCR jitter at the encoder


PCR Timestamp Issue (Contd.)PCR Timestamp Issue (Contd.)

What in your network facility could cause PCR timestamp issues?

Th f th t Three of the most common are:

It can happen any time you MUX streamsIt can happen any time you MUX streams

It can happen at the source encodingpp g

It can happen on any IP link – due to network laglag


PCR Jitter Due to IP CarriagePCR Jitter Due to IP Carriage

Network lag can conceal MPEG jitter problems on an IP link. The network jitter is usually so much larger than the PCR jitter that the PCR jitter is ‘lost in the noise.’the PCR jitter that the PCR jitter is lost in the noise.

Hopefully, the IP-ASI or IP-QAM edge device will id b ff i d ‘hi h l l th’ t thprovide buffering and use ‘high level math’ to smooth

out the network lag.

MT-40 provides a way to separate the Network Lag from PCR Jitter.



Q: What is the key element for Q: What is the key element for keeping the Encoder and Decoder inkeeping the Encoder and Decoder inkeeping the Encoder and Decoder in keeping the Encoder and Decoder in

time sync?time sync?


Video and Audio BuffersVideo and Audio Buffers& Presentation Time & Presentation Time Stamp (PTS)Stamp (PTS)Stamp (PTS)Stamp (PTS)


Presentation Time Stamp Presentation Time Stamp -- PTSPTS

Each Frame is marked with a PTS – “Presentation Time Stamp” – a positive number

Th l f th PTS i t t th l f th E d The value of the PTS is set to the value of the Encoder Clock when the frame is encoded

MPEG Packets

Encoder

27Mhz Clock

1,2,3,4…..

F1PTS 500

F2PTS 950

Packetizer


Packets Assigned to Decode BufferPackets Assigned to Decode Buffer

As packets flow into the Decoder, a space in memory is set aside for them, one buffer for each PID.

DecoderDecoderDecoder

MPEG Packets

Decoder

27Mhz Clock

Decoder

27Mhz Clock

Decoder

27Mhz Clock

1,2,3,4…..1,2,3,4…..1,2,3,4…..

Buffer 1 Pid 0x31 Video

Buffer 2 Pid 0x34 Audio


Reconstruction of Frames From BufferReconstruction of Frames From Buffer

Packets form Video and Audio Frames in the buffer


MPEG Packets

Decoder

27Mhz Clock

Decoder

27Mhz Clock

Decoder

27Mhz Clock

1,2,3,4…..1,2,3,4…..1,2,3,4…..


F1PTS 500

F2PTS 675

F3PTS 950


F1PTS 200

F2PTS 990


200 990

The Magic of DecodeThe Magic of Decode

When the value of the Decode clock MATCHES the PTS on the frame, that frame is sent to the decode hardware DecoderDecoderDecoderhardware

MPEG PacketsF1

Decode Hardware

Decoder

27Mhz Clock

Decoder

27Mhz Clock

Decoder

27Mhz Clock

F1PTS 200

= 200= 200= 200


F1PTS 500

F2PTS 675

F3PTS 950


F2PTS 990


990

Another Frame Goes to Decode HardwareAnother Frame Goes to Decode Hardware

Next Frame


MPEG PacketsF1PTS

Decode Hardware

Decoder

27Mhz Clock

Decoder

27Mhz Clock

Decoder

27Mhz Clock

PTS 500

= 500= 500= 500


F2PTS 675

F3PTS 950


F2PTS 990


990

One More Frame Heads to DecodeOne More Frame Heads to Decode

And the next frame…


MPEG PacketsF2PTS

Decode Hardware

Decoder

27Mhz Clock

Decoder

27Mhz Clock

Decoder

27Mhz Clock

PTS 675

= 675= 675= 675


F3PTS 950


F2PTS 990


990

Audio and Video BuffersAudio and Video Buffers

Receiver must buffer audio and video frame data until presentation time.

If d t t l t i th t t t b ff If data appears too late in the transport stream, buffer underflow results.

If data appears too early in the transport streamIf data appears too early in the transport stream, buffer overflow results.

Either condition results in garbled play or incorrect g p ysynchronization.

Different set top boxes may respond differently to the same underlying buffer violations


Summary: Audio/Video SyncSummary: Audio/Video Sync

PCR values help the Encoder Clock and the Decoder Clock to remain in sync

PCR jitt h i ti bl f PCR jitter can cause synchronization problems for elementary streams

EnsureEnsure PCR jitter and frequency offsets are within standard limits

Elementary stream buffers limits are NOT violated y

Large PCR jitter values can cause “Lip sync” error

Buffer over- or underflow problems may cause “tiling”,Buffer over or underflow problems may cause tiling , “pixelization”/”macroblocking” errors



Q: What is one potential result of Q: What is one potential result of “video buffer underflow” ?“video buffer underflow” ?



Three main monitoring and troubleshooting lessons: Fix Continuity Problems first C ti it t b l i th Continuity errors create bogus alarms in other areas


Check for PCR jitter PCR jitter can cause packet over- or underflow problems

Lip synch errors may also be result of PCR jitterLip synch errors may also be result of PCR jitter

To Be Discussed


MPEG T bl h tiMPEG T bl h tiMPEG TroubleshootingMPEG Troubleshootingusing the MTusing the MT--4040gg


Why Transport Stream Analyzer?Why Transport Stream Analyzer?

With analog transmission, if audio/video did not have any anomalies on a TV set up in the studio, it would show up intact on the end user’s TVshow up intact on the end user s TV

For digital transmission, this assumption is NOT valid di it l i l l th d d ’as digital signals rely on the decoder’s

Firmware implementation

Buffer sizesBuffer sizes

Software decoding capability


Why Transport Stream Analyzer? (Contd.)Why Transport Stream Analyzer? (Contd.)

The transition to digital has introduced some specific challenges for broadcast engineers

• Not all Set top boxes will respond the same way to the same underlying problem

• Standards violations in digital Transport Streams may show up on a i l i t itt tlreceiver only intermittently

The only streams which will consistently decode are those which are compliantp

The best way to assure compliance is with a Transport stream Analyzer/Monitor


Troubleshooting Example Troubleshooting Example –– Audio OutageAudio Outage Customer calls into station or NOC – audio dropping out on their set

In station video monitors & set top boxes do not have any problems

How serious is this problem? Are other Customers seeing it?

EncodersEncodersEncoders

EncodersEncoders

SatelliteR iS lli Network QAM

Satellite Dish

QPSK ReceiversSatelliteReceiversSatellite

Receivers

PSIP Gen

MUX NetworkProcessing

QAM Modulator

Digital to Analog Mod

Data GenCable TV Scenario


Troubleshooting Example (Contd.)Troubleshooting Example (Contd.)

Start at the end…..Off-air or combined RF output….


EncodersEncoders

SatelliteR iS t llit Network QAM

ASI

ASI

Satellite Dish


Receivers

PSIP Gen


QAM Modulator


ASI

ASI

ASI

Gigabit-IP


Transport StreamAnalyzer

RF Input (8VSB or QAM)


Troubleshooting Example (Contd.)Troubleshooting Example (Contd.) Check of the MPEG analyzer shows Standards violation has occurred



Encoders

Move back in the network toward the beginning.... Input to the QAM modulator………

EncodersEncoders

EncodersEncoders

SatelliteR iS t llit Network

QAM Modulator

ASI

ASIGigabit-IP

Satellite Dish


Receivers

PSIP Gen


Modulator


ASI

ASI

ASI

GigabitData Gen

Gigabit Ethernet

Input




Standards violation is still present



Encoders

Move further back…..

EncodersEncoders

EncodersEncoders


ASI

ASI

Satellite Dish


Receivers

PSIP Gen


QAM Modulator


ASI

ASI

Gigabit-IP

Data Gen ASIInput




Standards violation is still present



And further back…..


EncodersEncoders


ASI

ASI

Satellite Dish


Receivers

PSIP Gen


QAM Modulator


ASI

ASI

ASI

Gigabit-IP


ASIInput




Encoders

Using record capability to collect data…..

EncodersEncoders

EncodersEncoders


ASI

ASIGigabit-IP

Satellite Dish


Receivers

PSIP Gen


QAM Modulator


ASI

ASI

ASI

Data Gen

Cable TV Scenario

Record at this point

Record at this point


this point


Summary: MPEG Monitoring Over the Long TermSummary: MPEG Monitoring Over the Long Term

Encoders Broadcast Scenario

Complete and continous monitoring…..Analyze, Monitor or

Record Streams at any EncodersEncoders

EncodersEncoders

SatelliteR iS t llit Network

TelevisionTransmitter

Broadcast Scenario

ASI

ASIASI

Gigabit-IP,ASI or

SMPTE 310

of these points

Satellite Dish


Receivers

PSIP Gen


QAM Modulator

ASI

ASI

Gigabit-IP

Data GenModulator


Cable TV Scenario

Transport StreamAnalyzer or

Remote Monitor

RF Input (8VSB or QAM)Error Alerts:SNMP,SMS,E-Mail, Triggered Recording or

Error Notification


Triggered Recording orContact Closure


Three main monitoring and troubleshooting lessons: Fix Continuity Problems first C ti it t b l i th Continuity errors create bogus alarms in other areas


Check for PCR jitter PCR jitter can cause packet over- or underflow problems

Lip synch errors may also be result of PCR jitterLip synch errors may also be result of PCR jitter

Move Backward through your network as you debug Isolate the offending device first, then go for detailed problem

l i t ( di fil t )solving steps (recording a file, etc.)


Summary: MPEG’s 7 Basic ParametersSummary: MPEG’s 7 Basic Parameters

Per ATSC standards:

PAT Interval: 100ms

PMT Interval: 400ms

PCR Interval: 100ms

Max Jitter: 500ns

Max Freq. Offset: +/- 810 Hz

Also check:Video Buffer

Audio Buffer


ReferencesReferences

Information Technology -- Generic Coding of Moving Pictures and Associated Audio Information: Systems (MPEG-2 Systems

standard), ISO/IEC 13818-1.), /

ATSC Digital Television Standard, ATSC Doc. A/53.

Program and System Information Protocol for Terrestrial d d bl / ( h d )Broadcast and Cable, ATSC Doc. A/65 (with amendments).

ATSC Data Broadcast Standard, ATSC Doc. A/90.

ATSC A/78 Recommended Practice on Bitstream VerificationATSC A/78 Recommended Practice on Bitstream Verification.

Video Over IP by Wes Simpson – available SCTE bookstore.


In the Caribbean:

Mario [email protected]

I V l Add d R ll i th

@ pBernard How

[email protected]

Is our Value Added Re-seller in the Caribbean for Triveni Digital products

Stream Scope:p•MT-40 MPEG analyzer•RM-40 MPEG monitor

GuideBuilder – PSIP metadata generatorGuideBuilder SI metadata generator


GuideBuilder-SI -- metadata generator

Thank you-Gracias-Merci-Danki…

Caribbean Cable Television AssociationSan Juan, Puerto Rico August 17, 2011

MPEG 101 MPEG 101 ––Transport Stream Demystification Transport Stream Demystification


mpeg 101 demyst analysis & picture symptoms 20110808 opt

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