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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:
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Basic MPEG Building BlocksBasic MPEG Building Blocks
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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
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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
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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
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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)
MPEG-2 Transport Stream
AdaptationField
ContinuityCounter
SyncByte PID
188 Bytes
PES 1Adaptation
Field(Optional)
PIDSyncByte
ContinuityCounter PES x Or other Payload (Pat, PMT, PSIP,
etc)……………………………...
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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
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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
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MPEG Header Fields: Sync Byte (Contd.)MPEG Header Fields: Sync Byte (Contd.)
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
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MPEG Header Fields: Sync Byte (Contd.)MPEG Header Fields: Sync Byte (Contd.)
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
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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
MPEG-2 Transport Stream
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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
MPEG-2 Transport Stream
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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
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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
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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
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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 ?
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PSI Data In the StreamPSI Data In the Stream
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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
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MPEGMPEG--2 PSI Tables (Contd.)2 PSI Tables (Contd.)
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
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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
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PMT PID for PMT
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MPEGMPEG--2 PSI Tables (Contd.)2 PSI Tables (Contd.)
Decoder: Receiver or Set top Box
“WXXX Channel Video”PID 0x31
“WXXX Channel Audio”PID 0x34
PSIPID assignments
Th PIDS t th
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These PIDS go together
PSIP Data In the StreamPSIP Data In the Stream
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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
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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)
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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
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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
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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
188 BytesHeader (4 Bytes)
PES 1Adaptation
Field(Optional)
PIDSyncByte
ContinuityCounter PES x Or other Payload (Pat, PMT, PSIP,
etc)……………………………...
Payload
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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.
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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.
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PIDs in the StreamPIDs in the Stream
PAT points to PMT
PAT points
toPMT
PSIPPSIP metadata
tables: VCT, MGT, STT,
EITs & ETTs
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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
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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)
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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
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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.
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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
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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)
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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
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Continuity CounterContinuity Counter
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MPEG 101 Knowledge Check #2MPEG 101 Knowledge Check #2
Q: Name two tables found in PSI Q: Name two tables found in PSI metadatametadatametadatametadata
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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 ……
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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.
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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
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MPEG 101 Knowledge Check #3MPEG 101 Knowledge Check #3
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?
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Elementary streams:Elementary streams:yyEncoding Video & Audio Encoding Video & Audio DataDataDataData
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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:
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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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MPEGMPEG--2 Video/Audio Encoding2 Video/Audio Encoding
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
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MPEGMPEG--2 Video/Audio Encoding2 Video/Audio Encoding
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
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MPEGMPEG--2 Video/Audio Encoding2 Video/Audio Encoding
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
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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
188 BytesHeader (4 Bytes)
PES 1Adaptation
Field(Optional)
PIDSyncByte
ContinuityCounter PES x Or other Payload (Pat, PMT, PSIP,
etc)……………………………...
OptionalFieldsLength Flags Stuffing
BytesAdaptation Field on Video
PID’s Only
PCR
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MPEGMPEG--2 Video/Audio Encoding2 Video/Audio Encoding
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
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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
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MPEGMPEG--2 Video/Audio Encoding2 Video/Audio Encoding
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
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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.
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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.)
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MPEG 101 Knowledge Check #4MPEG 101 Knowledge Check #4
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?
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Video and Audio Video and Audio deo a d ud odeo a d ud oSyncronization using Syncronization using PCRPCRPCRPCR
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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
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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…
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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
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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…..
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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…..
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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…..
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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
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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
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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
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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
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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
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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
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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”
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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
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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
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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
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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
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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.
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MPEG 101 Knowledge Check #5MPEG 101 Knowledge Check #5
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?
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Video and Audio BuffersVideo and Audio Buffers& Presentation Time & Presentation Time Stamp (PTS)Stamp (PTS)Stamp (PTS)Stamp (PTS)
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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
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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
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Reconstruction of Frames From BufferReconstruction of Frames From Buffer
Packets form Video and Audio Frames in the buffer
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
F1PTS 500
F2PTS 675
F3PTS 950
Buffer 2 Pid 0x34 Audio
F1PTS 200
F2PTS 990
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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
Buffer 1 Pid 0x31 Video
F1PTS 500
F2PTS 675
F3PTS 950
Buffer 2 Pid 0x34 Audio
F2PTS 990
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990
Another Frame Goes to Decode HardwareAnother Frame Goes to Decode Hardware
Next Frame
DecoderDecoderDecoder
MPEG PacketsF1PTS
Decode Hardware
Decoder
27Mhz Clock
Decoder
27Mhz Clock
Decoder
27Mhz Clock
PTS 500
= 500= 500= 500
Buffer 1 Pid 0x31 Video
F2PTS 675
F3PTS 950
Buffer 2 Pid 0x34 Audio
F2PTS 990
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990
One More Frame Heads to DecodeOne More Frame Heads to Decode
And the next frame…
DecoderDecoderDecoder
MPEG PacketsF2PTS
Decode Hardware
Decoder
27Mhz Clock
Decoder
27Mhz Clock
Decoder
27Mhz Clock
PTS 675
= 675= 675= 675
Buffer 1 Pid 0x31 Video
F3PTS 950
Buffer 2 Pid 0x34 Audio
F2PTS 990
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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
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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
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MPEG 101 Knowledge Check #6MPEG 101 Knowledge Check #6
Q: What is one potential result of Q: What is one potential result of “video buffer underflow” ?“video buffer underflow” ?
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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
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
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MPEG T bl h tiMPEG T bl h tiMPEG TroubleshootingMPEG Troubleshootingusing the MTusing the MT--4040gg
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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
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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
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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
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Troubleshooting Example (Contd.)Troubleshooting Example (Contd.)
Start at the end…..Off-air or combined RF output….
EncodersEncodersEncoders
EncodersEncoders
SatelliteR iS t llit Network QAM
ASI
ASI
Satellite Dish
QPSK ReceiversSatelliteReceiversSatellite
Receivers
PSIP Gen
MUX NetworkProcessing
QAM Modulator
Digital to Analog Mod
ASI
ASI
ASI
Gigabit-IP
Data GenCable TV Scenario
Transport StreamAnalyzer
RF Input (8VSB or QAM)
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Troubleshooting Example (Contd.)Troubleshooting Example (Contd.) Check of the MPEG analyzer shows Standards violation has occurred
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Troubleshooting Example (Contd.)Troubleshooting Example (Contd.)
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
QPSK ReceiversSatelliteReceiversSatellite
Receivers
PSIP Gen
MUX NetworkProcessing
Modulator
Digital to Analog Mod
ASI
ASI
ASI
GigabitData Gen
Gigabit Ethernet
Input
Transport StreamAnalyzer
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Troubleshooting Example (Contd.)Troubleshooting Example (Contd.)
Standards violation is still present
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Troubleshooting Example (Contd.)Troubleshooting Example (Contd.)
Encoders
Move further back…..
EncodersEncoders
EncodersEncoders
SatelliteR iS t llit Network QAM
ASI
ASI
Satellite Dish
QPSK ReceiversSatelliteReceiversSatellite
Receivers
PSIP Gen
MUX NetworkProcessing
QAM Modulator
Digital to Analog Mod
ASI
ASI
Gigabit-IP
Data Gen ASIInput
Transport StreamAnalyzer
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Troubleshooting Example (Contd.)Troubleshooting Example (Contd.)
Standards violation is still present
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Troubleshooting Example (Contd.)Troubleshooting Example (Contd.)
And further back…..
EncodersEncodersEncoders
EncodersEncoders
SatelliteR iS t llit Network QAM
ASI
ASI
Satellite Dish
QPSK ReceiversSatelliteReceiversSatellite
Receivers
PSIP Gen
MUX NetworkProcessing
QAM Modulator
Digital to Analog Mod
ASI
ASI
ASI
Gigabit-IP
Data GenCable TV Scenario
ASIInput
Transport StreamAnalyzer
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Troubleshooting Example (Contd.)Troubleshooting Example (Contd.)
Encoders
Using record capability to collect data…..
EncodersEncoders
EncodersEncoders
SatelliteR iS t llit Network QAM
ASI
ASIGigabit-IP
Satellite Dish
QPSK ReceiversSatelliteReceiversSatellite
Receivers
PSIP Gen
MUX NetworkProcessing
QAM Modulator
Digital to Analog Mod
ASI
ASI
ASI
Data Gen
Cable TV Scenario
Record at this point
Record at this point
Transport StreamAnalyzer
this point
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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
QPSK ReceiversSatelliteReceiversSatellite
Receivers
PSIP Gen
MUX NetworkProcessing
QAM Modulator
ASI
ASI
Gigabit-IP
Data GenModulator
Digital to Analog Mod
Cable TV Scenario
Transport StreamAnalyzer or
Remote Monitor
RF Input (8VSB or QAM)Error Alerts:SNMP,SMS,E-Mail, Triggered Recording or
Error Notification
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Triggered Recording orContact Closure
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
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.)
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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
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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.
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In the Caribbean:
Mario Sebastianimsebastiani@incospec.com
I V l Add d R ll i th
@ pBernard How
bhow@incospec.com
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
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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
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