MPEG-2 Transport Stream

Transcription

1 MPEG-2 Transport Stream 數位電視系統原理及軟體技術 銘傳大學資工系 : 陳游利 徐武孝 Agenda Digital TV Broadcasting Packetized Elementary Stream () MPEG-2 System: Multiplexing Multiplexed Stream Transport Stream (TS)

2 Digital TV Broadcasting DTV Transmitter Source Source Encoder Channel Encoder Digital Modulation (Symbol Mapper) Channel Source 1 Source n Mpeg Coding Mpeg Coding ES ES Mux MPEG-2 Compression + Multiplexing TS FEC Mod. Channel Coding + Modulation + Up Converter Up Convert er Broadcasting Network 3 Agenda DTV Transmission Chain Packetized Elementary Stream () MPEG-2 System: Multiplexing Multiplexed Stream Transport Stream (TS)

3 MPEG-2 Packetization Using Coding Technologies to solve the transport problem Source Coding Channel Coding Source 1 Source n Mpeg Coding Mpeg Coding ES ES Packet ization Packet ization Mux MPEG-2 Compression + Packetization + Multiplexing TS FEC Mod. Channel Coding + Modulation + Up Converter Up Convert er Broadcasting Network 5 MPEG-2 System: & TS Syntax Encapsulation of video, audio or private data MPEG-2 video syntax Video Elementary Stream MPEG-2 System syntax Header Useful data Fixed or variable length Packetized Elementary Stream Transport Stream 6

4 MPEG-2 Compression Process Encoder Generates Access Units VideoAccessUnit is aframe (I,Bor P) ASequence ofaccess Units Elementary Stream (ES) Split Into Packets PacketizedElementary Stream () Either all video or all audio Variable length packets(64kb maximum) Header ContainsTiming Information PresentationTime Stamp (PTS) Whento display packet contents DecoderTime Stamp (DTS) Whento decode packetcontents 7 Packetized Elementary Streams Contains Only Audio or Video or Data Access Units- no programmeguide information Variable in size.maximum 64Kbytes. Header may contain Timing Information: Decoder Time Stamp (DTS) i.e. when to decode avideo AU and/or PresentationTime Stamp (PTS) i.e. when to present to the viewer adecoded video or audio AU For audio PTS refers to first AU in packet. For video DTS/PTS refers to AU containing first picture start code commencing in packet. 8

5 Packetized Elementary Streams Packetized Elementary Stream (): usually organized to contain an integral number of ES access units packet : variable sized block up to bytes per block Semantic definitions of fields in packet : 9 Packetized Elementary Streams 10

6 MPEG-2 傳輸封包標頭 packet start code prefix stream id packet length optional HEADER packet data bytes scrambling control priority data alignment indicator copyright original or copy 7 flags header data length optional fields stuffing bytes (FF) M*8 PTS DTS 40 (33) 40 (33) ESCR ES rate DSM trick mode additional copy info CRC (42) (22) (7) extension A Packetized Elementary Stream consists entirely of packets. The packet consists of a payload and a header. 11 MPEG-2: Packet Semantics Packet start code prefix : bit stream 0x well-known Stream IDs : 110x xxxx -audio stream number x xxxx 1110 yyyy -video stream number yyyy ECM stream EMM stream DSM-CC stream scrambling control : Defines whether scrambling is used, and the chosen scrambling method 12

7 MPEG-2: Packet Semantics priority : Indicates priority of the current packet Data alignment indicator : Indicates if the payload starts with a video or audio start code Copyright : Indicates if the payload is copyright protected Original/copy flag : Indicates if this is the original ES 13 MPEG-2: Packet Semantics PTS(Presentation Time Stamp), DTS(Decode Time Stamp) : For audio / video streams may be used to synchronize a set of elementary streams and control the rate at which they are replayed by the receiver ESCR (Elementary Stream Clock Reference) : indicates the intended time of arrival of the byte containing the last bit of the ESCR_base at the input of the -STD for streams 14

8 MPEG-2: Packet Semantics ES rate : Rate at which the ES was encoded Trick mode : indicates the video/audio is not the normal ES, e.g. after DSM-CC has signaled a replay Additional copyright information : CRC set to 1 to indicate a copyright ES Extension Information : may be used to support MPEG-1 streams 15 Packet Example 16

9 Agenda DTV Transmission Chain Packetized Elementary Stream () MPEG-2 System: Multiplexing Multiplexed Stream Transport Stream (TS) MPEG-2 Multiplexing Using Coding Technologies to solve the transport problem Source Coding Channel Coding Source 1 Source n Mpeg Coding Mpeg Coding ES ES Packet ization Packet ization Mux MPEG-2 Compression + Packetization + Multiplexing TS FEC Mod. Channel Coding + Modulation + Up Converter Up Convert er Broadcasting Network 18

10 MPEG-2 System: Multiplexing The systems part of this Recommendation International Standard addresses the combining of one or more elementary streams of video and audio, as well as other data, into single or multiple streams which are suitable for storage or transmission. 19 MPEG-2 System: Multiplexing ES containing Access Units I,B,P Video Audio Encoder Presentation Units Encoder Teletext Data ES ES MPEG Compression Layer PCR Data Packetiser Packetiser Packetiser Packetiser Timing DTS / PTS M U L T I P L E X E R Program Specific Information (PSI) or Service Information (DVB-SI) System Time Clock (STC) Transport Stream (TS) MPEG Systems Layer + DVB / ATSC / ARIB M O D U L A T O R DVB ATSC ISDB Basic Standards ETS (SI) ETR 290 ETR154 QPSK, OFDM QAM HM 8VSB 20

11 MPEG-2 System: Multiplexing Compression of Presentation Units to yield Access Units. Succession of AUs comprises an Elementary Stream (ES) Packetisation of an elementary stream to yield a packetised elementary stream () packets are usually aligned on access unit boundary packets can be variable length 21 MPEG-2 System: Multiplexing Distribution of packet content amongst a number of fixed size Transport Packets to form a Transport Stream (TS) Add Timing Information to & Transport Packets Add Programme Specific Information (PSI) Sequential output of transport packets forms an MPEG-2 Transport Stream with a Constant Bit Rate (CBR) 22

12 MPEG-2 System: Multiplexing Program 1 Audio Video PTS/ DTS Program 2 Audio Video MUX TS PTS/ DTS PAT PSI Section PMT NIT PTS: Presentation Time Stamp DTS: Decoding Time Stamp 23 MPEG-2 System: Multiplexing Video transport packets V V V V Audio transport packets A A A A Private data transport packets D D D D Service information transport packets SI SI SI SI Null transport packets N N N N V MPEG-2 transport stream V A V D SI 24

13 Agenda DTV Transmission Chain Packetized Elementary Stream () MPEG-2 System: Multiplexing Multiplexed Stream Transport Stream (TS) Multiplexing Stream V A D The (Packetized Elementary Streams) packets continuously flow into the payloads of the transport stream packets. MPEG Video Coder MPEG Audio Coder Packetizer Packetizer Video Data Packetizer Audio Program MUX Transport MUX Program Stream (Error free Media) Transport Stream 26

14 Multiplexed Stream 27 MPEG 2 System Layer -PS Program Stream Primarily intended for storage and retrieval from storage media Grouping of video, audio, and data that have a common time base Each program stream consists of only one program Useful in error freeenvironments Large packet size Packets size may be variable DVD standard uses the MPEG-2 Program Stream 28

15 MPEG 2 System Layer -PS Single Program TS (Audio and Video ) : 29 MPEG 2 System Layer -TS Transport Stream Fixed length packet size Intended for non error free environments Easier to detect start and end of frames Easy to recover from packet loss/corruption More difficult to produce and demultiplex than program stream 30

16 MPEG 2 System Layer -TS Transport Stream : combines one or more programs with one or more independent time bases into a single stream is designed for use in environments where errors are likely Transport Stream packets are 188 bytes in length 31 MPEG 2 System Layer -TS 32

17 MPEG 2 System Layer -TS 33 Relationship Between TS and PS 34

18 Agenda DTV Transmission Chain Packetized Elementary Stream () MPEG-2 System: Multiplexing Multiplexed Stream Transport Stream (TS) Components of MPEG and DVB 36

19 MPEG-2 Transport Stream Header Data 184 Bytes TS Header Payload TS Header Payload Packets) TS Header Payload 4 Bytes 184 Bytes (Discontinuous Sync Byte Transport Error Indicator Payload Unit Start Indicator Transport Transport Scrambling Priority Control PID Adaptation Field Control Continuity Counter Adaptati on Field + Payload 37 What is a Transport Stream? 38

20 Transport Stream Packets 188 Byte Packet 4 Byte Packet Header Adaptation Field (may not be present) Payload (may not be present) Fixed length of 188 bytes Packets contain one type of data only i.e video,audio, data, programme guide information. May also carry timing information (PCR) in optional adaptation field Every 4 Byte Header Contains following fields: sync byte 0x47 transport error indicator payload unit start indicator 39 Transport Stream Packets Transport priority PID Scrambling Control Adaptation field control Continuity Counter. Adaptation field used either for stuffing or for information. This is only stuffing method allowed for transport packets carrying packets. In transport packets carrying PSI information stuffing bytes of value 0xFF placed after the last byte of a section of information to the end of the packet. Null Packets 40

21 Transport Stream Packets The simplest form of timing in the Transport stream Is the continuity count timer a 4-bit counter One counter per PID Increments with each non-repeated packet of the same PID number 41 MPEG-2: TS Packet Syntax sync byte transport error indicator payload unit start indicator transport priority PID transport scrambling control adaptation field control continuity counter adaptation field payload Fixed length of each packet: 188 bytes adaptation field length discontinuity indicator random access indicator elementary stream priority indicator flags optional fields stuffing bytes 5 (N*8) : optional field PCR OPCR splice countdown transport private data length transport private data Adaptation Field Extension Length 3 flags optional fields 48 (33+9) (M*8) (33+9) 8 8 (3) ltw_valid flag ltw offset piecewise rate type splice DTS next au (22) 4 36 (33) 42

22 MPEG-2: TS Packet Semantics Semantic definition of fields in TS packet layer : Synchronization byte 0x47 Transport error indicator set to 1 to indicate that at least 1 uncorrectable bit error exists in the packet Payload unit start indicator indicates that TS packets carry packets or PSI data 43 MPEG-2: TS Packet Semantics PID indicates the type and number of the data stored in the packet payload PID table 0x0000 Program Association Table 0x0001 Conditional Access Table 0x0002~0x000F reserved 0x0010~ may be assigned as network_pid, Program_map_PID, elementary_pid 0x1FFE or for other purposes 0x1FFF NULL packet 44

23 PID - Packet Identifier & Numbers Each video or audio stream can be assigned a fixed PID number for the duration of the program This PID value can change as it goes through a remultiplexer Certain PID numbers must NEVER change (RESERVED) - e.g. the PAT on PID 0 is the anchor of the whole system Different systems reserve certain PIDS for specific tables also these PID s may have more than one table on them e.g in DVB 0 to 0x1d (29) is reserved PID 0x14 is time & date (TDT) and time offset tables (TOT) 45 MPEG-2: TS Packet Semantics Transport-scrambling control indicates the scrambling mode of the TS packet payload Adaptation field control 00 reserved for future use by ISO/IEC 01 no adaptation_field, payload only 10 adaptation_field only, no payload 11 adaptation_field followed by payload 46

24 MPEG-2: TS Packet Semantics PCR (Program Clock Reference) shall be valid for the time base of audio or video elementary stream OPCR (Original PCR) assists in the reconstruction of a single program TS from another TS 47 A TS Packet Header Example 48

25 Any Questions? 敬請多 多指教 49