| MPEG Transport Stream | |
|---|---|
| Filename extension | .ts, .tsv, .tsa, .m2t[1] |
| Internet media type | video/MP2T[2] |
| Uniform Type Identifier (UTI) | public.mpeg-2-transport-stream[3] |
| Developed by | MPEG |
| Initial release | 10 July 1995; 30 years ago (1995-07-10)[4] |
| Latest release | ISO/IEC 13818-1:2022 September 2022; 3 years ago (2022-09) |
| Type of format | Container format |
| Container for | Audio, video, data |
| Extended to | M2TS,TOD |
| Standard | ISO/IEC 13818-1, ITU-T Recommendation H.222.0[4] |
| Open format? | Yes |
| Free format? | Yes[5] |
MPEG transport stream (MPEG-TS,MTS) or simplytransport stream (TS) is a standarddigital container format for transmission and storage ofaudio,video, andProgram and System Information Protocol (PSIP) data.[6] It is used in broadcast systems such asDVB,ATSC andIPTV.
Transport stream specifies a container format encapsulatingpacketized elementary streams, witherror correction andsynchronization pattern features for maintaining transmission integrity when thecommunication channel carrying the stream isdegraded.
Transport streams differ from the similarly namedMPEG program stream in several important ways: program streams are designed for reasonably reliable media, such as discs (likeDVDs), while transport streams are designed for lessreliable transmission, namelyterrestrial orsatellite broadcast. Further, a transport stream may carry multiple programs.
Transport stream is specified inMPEG-2 Part 1, Systems, formally known asISO/IEC standard 13818-1 orITU-T Rec. H.222.0.[4]
A transport stream encapsulates a number of other substreams, oftenpacketized elementary streams (PESs) which in turn wrap themain data stream using the MPEG codec or any number of non-MPEG codecs (such asAC3 orDTS audio, andMJPEG orJPEG 2000 video), text and pictures for subtitles, tables identifying the streams, and even broadcaster-specific information such as anelectronic program guide. Many streams are often mixed together, such as several different television channels, or multipleangles 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 toprogram streams and other common containers such asAVI,MOV/MP4, andMKV, 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 asconstant bitrate (CBR) and filled with padding bytes when not enough data exists.[a]
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Anetwork packet is the basic unit of data in a transport stream, and a transport stream is merely a sequence of packets. Each packet starts with async byte and aheader, which may be followed by optional additional headers; the rest of the packet consists ofpayload. All header fields are read asbig-endian. Packets are 188 bytes in length, but the communication medium may add additional information.[b] The 188-byte packet size was originally chosen for compatibility withAsynchronous Transfer Mode (ATM) systems.[8][9]
| Name | Number of bits | Bitmask (big-endian) | Description |
|---|---|---|---|
| 4-byte Transport Stream Header | |||
| Sync byte | 8 | 0xff000000 | Bit pattern of 0x47 (ASCII char 'G') |
| Transport error indicator (TEI) | 1 | 0x800000 | Set when ademodulator can't correct errors from FEC data; indicating the packet is corrupt.[10] |
| Payload unit start indicator (PUSI) | 1 | 0x400000 | Set when this packet contains the first byte of a new payload unit. ForPSI packet data, the first byte of the payload will indicate where this new payload unit starts. ForPES packet data, the new PES packet shall start at the start of the payload.[11] This field allows a receiver that started reading mid transmission to know when it can start extracting data. |
| Transport priority | 1 | 0x200000 | Set when the current packet has a higher priority than other packets with the same PID. |
| PID | 13 | 0x1fff00 | Packet Identifier, describing the payload data. |
| Transport scrambling control (TSC) | 2 | 0xc0 | '00' = Not scrambled. ForDVB-CSA andATSC DES only:[12] |
| Adaptation field control | 2 | 0x30 | 01 – no adaptation field, payload only, 10 – adaptation field only, no payload, |
| Continuity counter | 4 | 0xf | Sequence number of payload packets(0x00 to 0x0F) within each stream (except PID 8191) Incremented per-PID, only when a payload flag is set. |
| Optional fields | |||
| Adaptation field | variable | Present ifadaptation field control is 10 or 11. See below for format. | |
| Payload data | variable | Present ifadaptation field control is 01 or 11. Payload may be PES packets, program specific information (below), or other data. | |
| Name | Number of bits | Bitmask | Description |
|---|---|---|---|
| Adaptation field length | 8 | Number of bytes in the adaptation field immediately following this byte | |
| Discontinuity indicator | 1 | 0x80 | Set if current TS packet is in a discontinuity state with respect to either the continuity counter or the program clock reference |
| Random access indicator | 1 | 0x40 | Set when the stream may be decoded without errors from this point |
| Elementary stream priority indicator | 1 | 0x20 | Set when this stream should be considered "high priority" |
| PCR flag | 1 | 0x10 | Set when PCR field is present |
| OPCR flag | 1 | 0x08 | Set when OPCR field is present |
| Splicing point flag | 1 | 0x04 | Set when splice countdown field is present |
| Transport private data flag | 1 | 0x02 | Set when transport private data is present |
| Adaptation field extension flag | 1 | 0x01 | Set when adaptation extension data is present |
| Optional fields | |||
| PCR | 48 | Program clock reference, stored as 33 bits base, 6 bits reserved, 9 bits extension. The value is calculated as base * 300 + extension. | |
| OPCR | 48 | Original Program clock reference. Helps when one TS is copied into another | |
| Splice countdown | 8 | Indicates how many TS packets from this one a splicing point occurs (Two's complement signed; may be negative) | |
| Transport private data length | 8 | The length of the following field | |
| Transport private data | variable | Private data | |
| Adaptation extension | variable | See below | |
| Stuffing bytes | variable | Always0xFF | |
| Name | Number of bits | Bitmask | Description |
|---|---|---|---|
| Adaptation extension length | 8 | 0xff00 | The length of the header |
| Legal time window (LTW) flag | 1 | 0x0080 | |
| Piecewise rate flag | 1 | 0x0040 | |
| Seamless splice flag | 1 | 0x0020 | |
| Reserved | 5 | 0x001f | |
| Optional fields | |||
| LTW flag set (2 bytes) | |||
| LTW valid flag | 1 | 0x8000 | |
| LTW offset | 15 | 0x7fff | Extra information for rebroadcasters to determine the state of buffers when packets may be missing. |
| Piecewise flag set (3 bytes) | |||
| Reserved | 2 | 0xc00000 | |
| Piecewise rate | 22 | 0x3fffff | The rate of the stream, measured in 188-byte packets, to define the end-time of the LTW. |
| Seamless splice flag set (5 bytes) | |||
| Splice type | 4 | 0xf000000000 | Indicates the parameters of the H.262 splice. |
| DTS next access unit | 36 | 0x0efffefffe | The PES DTS of the splice point. Split up as multiple fields, 1 marker bit (0x1), 15 bits, 1 marker bit, 15 bits, and 1 marker bit, for 33 data bits total. |
| Name | Number of bits | Bitmask | Description |
|---|---|---|---|
| Payload Pointer (optional) | 8 | 0xff | Present only if the Payload Unit Start Indicator (PUSI) flag is set, and the packet data type is PSI (not PES). It gives the index after this byte at which the new payload unit starts. Any payload byte before the index is part of the previous payload unit. |
| Actual Payload | variable | The content of the payload. |
Each table or elementary stream in a transport stream is identified by a 13-bit packet identifier (PID). Ademultiplexer 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.
| Decimal | Hexadecimal | Description |
|---|---|---|
| 0 | 0x0000 | Program association table (PAT) contains a directory listing of all program map tables |
| 1 | 0x0001 | Conditional access table (CAT) contains a directory listing of all ITU-T Rec. H.222 entitlement management message streams used by program map tables |
| 2 | 0x0002 | Transport stream description table (TSDT) contains descriptors relating to the overall transport stream |
| 3 | 0x0003 | IPMP control information table contains a directory listing of all ISO/IEC 14496-13 control streams used by program map tables |
| 4–15 | 0x0004-0x000F | Reserved for future use |
| 16–31 | 0x0010-0x001F | Used byDVBmetadata[14]
|
| 32-8186 | 0x0020-0x1FFA | May be assigned as needed to program map tables, elementary streams and other data tables |
| 8187 | 0x1FFB | Used byDigiCipher 2/ATSC MGTmetadata |
| 8188–8190 | 0x1FFC-0x1FFE | May be assigned as needed to program map tables, elementary streams and other data tables |
| 8191 | 0x1FFF | Null Packet (used for fixed bandwidth padding) |
Transport stream has a concept ofprograms. 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. Areceiver 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).
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.
To enable a decoder to present synchronized content, such as audio tracks matching the associated video, at least once each 100 ms, aprogram 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 thepcr_pid value in the associated PMT. The value of the PCR, when properly used, is employed to generate asystem_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, thepresentation 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 bits are based on a 27 MHz clock. The maximum jitter permitted for the PCR is+/- 500 ns.
Some transmission schemes, such as those inATSC andDVB, 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 null packets have a payload that is filled with 0xFF, and the receiver is expected to ignore its contents.[15]
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.[16][17] This is what is informally calledM2TS stream, commonly found inHDV cameras. The timecode allows quick access to any part of the stream, either from a media player or from a non-linear video editing system.[18]
JVC called M2TS "TOD"[c] when used in HDD-based camcorders likeGZ-HD7.[19][20] It is also used to synchronize video streams from several cameras in amultiple-camera setup.
Blu-ray Disc video titles authored with menu support are in theBlu-ray Disc Movie (BDMV) format and contain audio, video, and other streams in a BDAV container, which is based on the M2TS format.[21][22] TheBlu-ray Disc Association calls it "BDAV MPEG-2 transport stream".[16] 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 onBlu-ray Disc recordable for audio/video recording.[22][d] 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.[17] 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.[17][24]
Licenses pertain to tools and not to streams or files per se.
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