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TS

MPEG transport stream

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MPEG Transport Stream Filename extension         .ts

Internet media type        video/MP2T

Developed by           MPEG

Initial release           1995

Type of format         Media container

Container for Audio, video, data

Extended to    M2TS, TOD

Standard(s)     ISO/IEC 13818-1, ITU-T Recommendation H.222.0

MPEG transport stream (TS) is a standard format for transmission and storage of audio, video, and Program and System Information Protocol (PSIP) data, and is used in broadcast systems such as DVB and ATSC.

Transport Stream is specified in MPEG-2 Part 1, Systems (formally known as ISO/IEC standard 13818-1 or ITU-T Rec. H.222.0).

Transport stream specifies a container format encapsulating packetized elementary streams, with error correction and stream synchronization features for maintaining transmission integrity when the signal is degraded.

Transport streams differ from the similarly named Program Streams in several important ways: Program Streams, also called PS, are designed for reasonably reliable media, such as discs (like DVDs), while TS is designed for less reliable transmission, namely terrestrial or satellite broadcast. Further, a Transport Stream may carry multiple Programs.

Important elements of a transport stream

Packet

A packet is the basic unit of data in a transport stream. It consists of a sync byte, whose value is 0x47, followed by three one-bit flags and a 13-bit Packet Identifier (PID). This is followed by a 4-bit continuity counter. Additional optional transport fields, as signaled in the optional adaptation field, may follow. The rest of the packet consists of payload. Packets are 188 bytes in length, but the communication medium may add some error correction bytes to the packet. ISDB-T and DVB-T/C/S uses 204 bytes and ATSC 8-VSB, 208 bytes as the size of emission packets (transport stream packet + FEC data). ATSC transmission adds 20 bytes of Reed-Solomon forward error correction to create a packet that is 208 bytes long. The 188-byte packet size was originally chosen for compatibility with ATM systems.

PID

Each table or elementary stream in a transport stream is identified by a 13-bit packet ID (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 will be used to decide how often a particular PID appears in the transport stream.

Programs

Transport stream has a concept of programs. Each single program is described by a Program Map Table (PMT) which has a unique PID, and the elementary streams associated with that program have PIDs listed in the PMT. 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 a particular "channel" 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 MPTS - Multi Program Transport Stream. A single program transport stream is referred to as SPTS.

Program Specific Information (PSI)

Main article: Program Specific Information

There are 4 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.

PAT

PAT stands for Program Association Table. It lists all programs available in the transport stream. Each of the listed programs is identified by a 16-bit value called program_number. Each of the programs listed in PAT has an associated value of PID for its Program Map Table (PMT).

The value 0x0000 of program_number is reserved to specify the PID where to look for Network Information Table (NIT). If such a program is not present in PAT the default PID value (0x0010) shall be used for NIT.

TS Packets containing PAT information always have PID 0x0000.

PMT

Program Map Tables (PMTs) contain information about programs. For each program, there is one PMT. While the MPEG-2 standard permits more than one PMT section to be transmitted on a single PID, most MPEG-2 "users" such as ATSC and SCTE require each PMT to be transmitted on a separate PID that is not used for any other packets. The PMTs provide information on each program present in the transport stream, including the program_number, and list the elementary streams that comprise the described MPEG-2 program. There are also locations for optional descriptors that describe the entire MPEG-2 program, as well as an optional descriptor for each elementary stream. Each elementary stream is labeled with a stream_type value.

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, or 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 Program Map Table. The value of the PCR, when properly used, is employed to generate a system_timing_clock in the decoder. The STC decoder, when properly implemented, provides a highly accurate time base that is used to synchronize audio and video elementary streams. Timing in MPEG2 references this clock, for example the presentation time stamp (PTS) is intended to be relative to the PCR. The first 33 bits are based on a 90 kHz clock. The last 9 are based on a 27 MHz clock. The maximum jitter permitted for the PCR is +/- 500 ns.

Null packets

Some transmission schemes, such as those in ATSC and DVB, 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 may not contain any data at all, and the receiver is expected to ignore its contents.

Moving Picture Experts Group

From Wikipedia, the free encyclopedia

  (Redirected from MPEG)

MPEG logo

"MPEG" redirects here. For the guild, see Motion Picture Editors Guild. For the unaffiliated company that licenses patent pools for some MPEG standards, see MPEG LA.

MPEG.svg

The Moving Picture Experts Group (MPEG) is a working group of experts that was formed by ISO and IEC to set standards for audio and video compression and transmission. It was established in 1988 by the initiative of Hiroshi Yasuda (Nippon Telegraph and Telephone) and Leonardo Chiariglione, who has been from the beginning the Chairman of the group. The first MPEG meeting was in May 1988 in Ottawa, Canada. As of late 2005, MPEG has grown to include approximately 350 members per meeting from various industries, universities, and research institutions. MPEG's official designation is ISO/IEC JTC1/SC29 WG11 - Coding of moving pictures and audio (ISO/IEC Joint Technical Committee 1, Subcommittee 29, Working Group 11).

Overview

Compression methodology

The MPEG compression methodology is considered asymmetric as the encoder is more complex than the decoder. The encoder needs to be algorithmic or adaptive whereas the decoder is 'dumb' and carries out fixed actions. This is considered advantageous in applications such as broadcasting where the number of expensive complex encoders is small but the number of simple inexpensive decoders is large. The MPEG's (ISO's) approach to standardization is novel, because it is not the encoder that is standardized, but the way a decoder interprets the bitstream. A decoder that can successfully interpret the bitstream is said to be compliant. The advantage of standardizing the decoder is that over time encoding algorithms can improve, yet compliant decoders continue to function with them. The MPEG standards give very little information regarding structure and operation of the encoder and implementers can supply encoders using proprietary algorithms. This gives scope for competition between different encoder designs, which means better designs, can evolve and users have greater choice, because encoders of different levels of cost and complexity can exist, yet a compliant decoder operates with all of them.

MPEG also standardizes the protocol and syntax under which it is possible to combine or multiplex audio data with video data to produce a digital equivalent of a television program. Many such programs can be multiplexed and MPEG defines the way such multiplexes can be created and transported. The definitions include the metadata used by decoders to demultiplex correctly.

Standards

The MPEG standards consist of different Parts. Each part covers a certain aspect of the whole specification. The standards also specify Profiles and Levels. Profiles are intended to define a set of tools that are available, and Levels define the range of appropriate values for the properties associated with them. Some of the approved MPEG standards were revised by later amendments and/or new editions. MPEG has standardized the following compression formats and ancillary standards:

    MPEG-1 (1993): Coding of moving pictures and associated audio for digital storage media at up to about 1,5 Mbit/s (ISO/IEC 11172). The first MPEG compression standard for audio and video. It is commonly limited to about 1.5 Mbit/s although the specification is capable of much higher bit rates. It was basically designed to allow moving pictures and sound to be encoded into the bitrate of a Compact Disc. It is used on Video CD, SVCD and can be used for low-quality video on DVD Video. It was used in digital satellite/cable TV services before MPEG-2 became widespread. To meet the low bit requirement, MPEG-1 downsamples the images, as well as uses picture rates of only 24–30 Hz, resulting in a moderate quality. It includes the popular MPEG-1 Audio Layer III (MP3) audio compression format.

    MPEG-2 (1995): Generic coding of moving pictures and associated audio information (ISO/IEC 13818). Transport, video and audio standards for broadcast-quality television. MPEG-2 standard was considerably broader in scope and of wider appeal – supporting interlacing and high definition. MPEG-2 is considered important because it has been chosen as the compression scheme for over-the-air digital television ATSC, DVB and ISDB, digital satellite TV services like Dish Network, digital cable television signals, SVCD and DVD Video. It is also used on Blu-ray Discs, but these normally use MPEG-4 Part 10 or SMPTE VC-1 for high-definition content.

    MPEG-3: MPEG-3 dealt with standardizing scalable and multi-resolution compression and was intended for HDTV compression but was found to be redundant and was merged with MPEG-2, as a result there is no MPEG-3 standard. MPEG-3 is not to be confused with MP3, which is MPEG-1 Audio Layer 3.

    MPEG-4 (1998): Coding of audio-visual objects. (ISO/IEC 14496) MPEG-4 uses further coding tools with additional complexity to achieve higher compression factors than MPEG-2. In addition to more efficient coding of video, MPEG-4 moves closer to computer graphics applications. In more complex profiles, the MPEG-4 decoder effectively becomes a rendering processor and the compressed bitstream describes three-dimensional shapes and surface texture. MPEG-4 supports Intellectual Property Management and Protection (IPMP), which provides the facility to use proprietary technologies to manage and protect content like digital rights management. It also supports MPEG-J, a fully programmatic solution for creation of custom interactive multimedia applications (Java application environment with a Java API) and many other features. Several new higher-efficiency video standards (newer than MPEG-2 Video) are included, notably:

        MPEG-4 Part 2 (or Simple and Advanced Simple Profile) and

        MPEG-4 AVC (or MPEG-4 Part 10 or H.264). MPEG-4 AVC may be used on HD DVD and Blu-ray Discs, along with VC-1 and MPEG-2.

In addition, the following standards, while not sequential advances to the video encoding standard as with MPEG-1 through MPEG-4, are referred to by similar notation:

    MPEG-7 (2002): Multimedia content description interface. (ISO/IEC 15938)

    MPEG-21 (2001): Multimedia framework (MPEG-21). (ISO/IEC 21000) MPEG describes this standard as a multimedia framework and provides for intellectual property management and protection.

Moreover, more recently than other standards above, MPEG has started following international standards; each of the standards holds multiple MPEG technologies for a way of application. (For example, MPEG-A includes a number of technologies on multimedia application format.)

    MPEG-A (2007): Multimedia application format (MPEG-A). (ISO/IEC 23000) (e.g., Purpose for multimedia application formats, MPEG music player application format, MPEG photo player application format and others)

    MPEG-B (2006): MPEG systems technologies. (ISO/IEC 23001) (e.g., Binary MPEG format for XML, Fragment Request Units, Bitstream Syntax Description Language (BSDL) and others)

    MPEG-C (2006): MPEG video technologies. (ISO/IEC 23002) (e.g., Accuracy requirements for implementation of integer-output 8x8 inverse discrete cosine transform and others)

    MPEG-D (2007): MPEG audio technologies. (ISO/IEC 23003) (e.g., MPEG Surround, SAOC-Spatial Audio Object Coding and USAC-Unified Speech and Audio Coding)

    MPEG-E (2007): Multimedia Middleware. (ISO/IEC 23004) (a.k.a. M3W) (e.g., Architecture, Multimedia application programming interface (API), Component model and others)

Supplemental media technologies (2008). (ISO/IEC 29116) Part 1: Media streaming application format protocols will be revised in MPEG-M Part 4 - MPEG extensible middleware (MXM) protocols.

    MPEG-V (2011): Media context and control. (ISO/IEC 23005) (a.k.a. Information exchange with Virtual Worlds) (e.g., Avatar characteristics, Sensor information, Architecture and others)

    MPEG-M (2010): MPEG eXtensible Middleware (MXM). (ISO/IEC 23006) (e.g., MXM architecture and technologies, API, MPEG extensible middleware (MXM) protocols)

MPEG-U (2010): Rich media user interfaces. (ISO/IEC 23007) (e.g., Widgets)