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MPEG transport stream (MPEG-TS, MTS) or simply transport stream (TS) is a standard digital container format for transmission and storage of
audio Audio most commonly refers to sound, as it is transmitted in signal form. It may also refer to: Sound *Audio signal, an electrical representation of sound *Audio frequency, a frequency in the audio spectrum * Digital audio, representation of sou ...
,
video Video is an electronic medium for the recording, copying, playback, broadcasting, and display of moving visual media. Video was first developed for mechanical television systems, which were quickly replaced by cathode-ray tube (CRT) sy ...
, and Program and System Information Protocol (PSIP) data. It is used in broadcast systems such as
DVB Digital Video Broadcasting (DVB) is a set of international open standards for digital television. DVB standards are maintained by the DVB Project, an international industry consortium, and are published by a Joint Technical Committee (JTC) o ...
,
ATSC Advanced Television Systems Committee (ATSC) standards are an American set of standards for digital television transmission over terrestrial, cable and satellite networks. It is largely a replacement for the analog NTSC standard and, like th ...
and
IPTV Internet Protocol television (IPTV) is the delivery of television content over Internet Protocol (IP) networks. This is in contrast to delivery through traditional terrestrial, satellite, and cable television formats. Unlike downloaded med ...
. Transport stream specifies a container format encapsulating packetized elementary streams, with
error correction In information theory and coding theory with applications in computer science and telecommunication, error detection and correction (EDAC) or error control are techniques that enable reliable delivery of digital data over unreliable communi ...
and synchronization pattern features for maintaining transmission integrity when the
communication channel A communication channel refers either to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel in telecommunications and computer networking. A channel is used for informa ...
carrying the stream is degraded. Transport streams differ from the similarly-named
MPEG program stream Program stream (PS or MPEG-PS) is a container format for multiplexing digital audio, video and more. The PS format is specified in MPEG-1 Part 1 (ISO/IEC 11172-1) and MPEG-2 Part 1, Systems (ISO/IEC standard 13818-1/ITU-T H.222.0). The MPEG-2 ...
in several important ways: program streams are designed for reasonably reliable media, such as discs (like DVDs), while transport streams are designed for less reliable transmission, namely terrestrial or satellite broadcast. Further, a transport stream may carry multiple programs. Transport stream is specified in ''
MPEG-2 MPEG-2 (a.k.a. H.222/H.262 as was defined by the ITU) is a standard for "the generic coding of moving pictures and associated audio information". It describes a combination of lossy video compression and lossy audio data compression methods, ...
Part 1, Systems'', formally known as '' ISO/IEC standard 13818-1'' or ''
ITU-T The ITU Telecommunication Standardization Sector (ITU-T) is one of the three sectors (divisions or units) of the International Telecommunication Union (ITU). It is responsible for coordinating standards for telecommunications and Information Co ...
Rec. H.222.0''.


Overview

A transport stream encapsulates a number of other substreams, often packetized elementary streams (PESs) which in turn wrap the main data stream using the MPEG codec or any number of non-MPEG codecs (such as AC3 or DTS audio, and MJPEG or
JPEG 2000 JPEG 2000 (JP2) is an image compression standard and coding system. It was developed from 1997 to 2000 by a Joint Photographic Experts Group committee chaired by Touradj Ebrahimi (later the JPEG president), with the intention of superseding th ...
video), text and pictures for subtitles, tables identifying the streams, and even broadcaster-specific information such as an electronic program guide. Many streams are often mixed together, such as several different television channels, or multiple angles of a movie. Each stream is chopped into (at most) 188-byte sections and interleaved together. Due to the tiny packet size, streams can be interleaved with less latency and greater error resilience compared to program streams and other common containers such as
AVI Avi is a given name, usually masculine, often a diminutive of Avram, Avraham, etc. It is sometimes feminine and a diminutive of the Hebrew spelling of Abigail. People with the given name include: * Avi (born 1937), Newbery award-winning Americ ...
, MOV/ MP4, and MKV, which generally wrap each frame into one packet. This is particularly important for videoconferencing, where large frames may introduce unacceptable audio delay. Transport streams tend to be broadcast as
constant bitrate Constant bitrate (CBR) is a term used in telecommunications, relating to the quality of service. Compare with variable bitrate. When referring to codecs, constant bit rate encoding means that the rate at which a codec's output data should be ...
(CBR) and filled with padding bytes when not enough data exists.


Elements


Packet

A
network packet In telecommunications and computer networking, a network packet is a formatted unit of data carried by a packet-switched network. A packet consists of control information and user data; the latter is also known as the ''payload''. Control inform ...
is the basic unit of data in a transport stream, and a transport stream is merely a sequence of packets. Each packet starts with a sync byte and a header, that may be followed with optional additional headers; the rest of the packet consists of
payload Payload is the object or the entity which is being carried by an aircraft or launch vehicle. Sometimes payload also refers to the carrying capacity of an aircraft or launch vehicle, usually measured in terms of weight. Depending on the nature of ...
. All header fields are read as
big-endian In computing, endianness, also known as byte sex, is the order or sequence of bytes of a word of digital data in computer memory. Endianness is primarily expressed as big-endian (BE) or little-endian (LE). A big-endian system stores the most si ...
. Packets are 188 bytes in length, but the communication medium may add additional information. The 188-byte packet size was originally chosen for compatibility with Asynchronous Transfer Mode (ATM) systems.


Packet identifier (PID)

Each table or elementary stream in a transport stream is identified by a 13-bit packet identifier (PID). A demultiplexer extracts elementary streams from the transport stream in part by looking for packets identified by the same PID. In most applications,
time-division multiplexing Time-division multiplexing (TDM) is a method of transmitting and receiving independent signals over a common signal path by means of synchronized switches at each end of the transmission line so that each signal appears on the line only a fracti ...
will be used to decide how often a particular PID appears in the transport stream.


Programs

Transport stream has a concept of ''programs''. Every program is described by a program map table (PMT). The elementary streams associated with that program have PIDs listed in the PMT. Another PID is associated with the PMT itself. For instance, a transport stream used in digital television might contain three programs, to represent three television channels. Suppose each channel consists of one video stream, one or two audio streams, and any necessary metadata. A receiver wishing to decode one of the three channels merely has to decode the payloads of each PID associated with its program. It can discard the contents of all other PIDs. A transport stream with more than one program is referred to as a multi-program transport stream (MPTS). A single program transport stream is referred to as a single-program transport stream (SPTS).


Program specific information

There are 4 program specific information (PSI) tables: program association (PAT), program map (PMT), conditional access (CAT), and network information (NIT). The MPEG-2 specification does not specify the format of the CAT and NIT.


PCR

To enable a decoder to present synchronized content, such as audio tracks matching the associated video, at least once each 100 ms, a ''program clock reference'' (PCR) is transmitted in the adaptation field of an MPEG-2 transport stream packet. The PID with the PCR for an MPEG-2 program is identified by the ''pcr_pid'' value in the associated PMT. The value of the PCR, when properly used, is employed to generate a ''system_timing_clock'' in the decoder. The system time clock (STC) decoder, when properly implemented, provides a highly accurate time base that is used to synchronize audio and video elementary streams. Timing in MPEG-2 references this clock. For example, the
presentation time stamp The presentation timestamp (PTS) is a timestamp metadata field in an MPEG transport stream or MPEG program stream that is used to achieve synchronization of programs' separate elementary streams (for example Video, Audio, Subtitles) when present ...
(PTS) is intended to be relative to the PCR. The first 33 bits are based on a 90 kHz clock. The last 9 bits are based on a 27 MHz clock. The maximum jitter permitted for the PCR is .


Null packets

Some transmission schemes, such as those in
ATSC Advanced Television Systems Committee (ATSC) standards are an American set of standards for digital television transmission over terrestrial, cable and satellite networks. It is largely a replacement for the analog NTSC standard and, like th ...
and
DVB Digital Video Broadcasting (DVB) is a set of international open standards for digital television. DVB standards are maintained by the DVB Project, an international industry consortium, and are published by a Joint Technical Committee (JTC) o ...
, impose strict constant bitrate requirements on the transport stream. In order to ensure that the stream maintains a constant bitrate, a multiplexer may need to insert some additional packets. The PID 0x1FFF is reserved for this purpose. The payload of null packets is all zeroes, and the receiver is expected to ignore its contents.


Use in digital video cameras

Transport Stream was originally designed for broadcast. Later it was adapted for use with digital video cameras, recorders and players by adding a 4-byte timecode (TC) field to the standard 188-byte packets, resulting in a 192-byte packet. This is what is informally called M2TS stream. The
Blu-ray Disc Association The Blu-ray Disc Association (BDA) is the industry consortium that develops and licenses Blu-ray Disc technology and is responsible for establishing format standards and promoting business opportunities for Blu-ray Disc. The BDA is divided into th ...
calls it " BDAV MPEG-2 transport stream". JVC called it TOD when used in HDD-based camcorders like GZ-HD7. The timecode allows quick access to any part of the stream either from a media player, or from a non-linear video editing system. It is also used to synchronize video streams from several cameras in a
multiple-camera setup The multiple-camera setup, multiple-camera mode of production, multi-camera or simply multicam is a method of filmmaking and video production. Several cameras—either film or professional video cameras—are employed on the set and simultaneou ...
.


Use in Blu-ray

Blu-ray Disc video titles authored with menu support are in the Blu-ray Disc Movie (BDMV) format and contain audio, video, and other streams in a BDAV container, which is based on the MPEG-2 transport stream format.Afterdawn.co
Glossary – BD-MV (Blu-ray Movie) and BDAV container
, Retrieved on 26 July 2009
Afterdawn.co
Glossary – BDAV container
Retrieved on 26 July 2009
Blu-ray Disc video uses these modified MPEG-2 transport streams, compared to DVD's program streams that don't have the extra transport overhead. There is also the BDAV (Blu-ray Disc Audio/Visual) format, the consumer-oriented alternative to the BDMV format used for movie releases. The BDAV format is used on Blu-ray Disc recordable for audio/video recording. Blu-ray Disc employs the MPEG-2 transport stream recording method. This enables transport streams of a BDAV converted digital broadcast to be recorded as they are with minimal alteration of the packets. It also enables simple stream cut style editing of a BDAV converted digital broadcast that is recorded as is and where the data can be edited just by discarding unwanted packets from the stream. Although it is quite natural, a function for high-speed and easy-to-use retrieval is built in.Blu-ray Disc Association (August 2004
Blu-ray Disc Format, White paper
(PDF) Page 22, Retrieved on 28 July 2009


See also

* MPEG media transport (MMT) *
Real-time Transport Protocol The Real-time Transport Protocol (RTP) is a network protocol for delivering audio and video over IP networks. RTP is used in communication and entertainment systems that involve streaming media, such as telephony, video teleconference applicati ...
(RTP) * Unidirectional Lightweight Encapsulation (ULE)


Notes


References


External links


ITU-T H.222.0 , ISO/IEC 13818-1 Systems Spec Documents

Latest free copy of the spec, August 2018



TSDuck
– Free open-source tool to manipulate MPEG transport streams. {{DEFAULTSORT:Mpeg Transport Stream ATSC Digital container formats MPEG-2 ITU-T recommendations