MPEG transport stream (MPEG-TS, MTS) or simply transport stream (TS) is a standard digital container format for transmission and storage of audio, video, and Program and System Information Protocol (PSIP) data. It is used in broadcast systems such as DVB, ATSC and IPTV.
Transport stream specifies a container format encapsulating packetized elementary streams, with error correction and synchronization pattern features for maintaining transmission integrity when the communication channel carrying the stream is degraded.
Transport streams differ from the similarly named MPEG program stream 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 Part 1, Systems, formally known as ISO/IEC standard 13818-1 or ITU-T 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 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, 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 (CBR) and filled with padding bytes when not enough data exists.
Elements
Packet A network 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 a sync byte and a header, which may be followed by optional additional headers; the rest of the packet consists of payload. All header fields are read as big-endian. 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.
+ Partial transport stream packet formatNameNumber of bitsBitmask (big-endian)Description4-byte Transport Stream HeaderSync byte80xff000000Bit pattern of 0x47 (ASCII char 'G')Transport error indicator (TEI)10x800000Set when a demodulator can't correct errors from FEC data; indicating the packet is corrupt.Payload unit start indicator (PUSI)10x400000Set when this packet contains the first byte of a new payload unit. For PSI packet data, the first byte of the payload will indicate where this new payload unit starts. For PES packet data, the new PES packet shall start at the start of the payload. This field allows a receiver that started reading mid transmission to know when it can start extracting data.Transport priority10x200000Set when the current packet has a higher priority than other packets with the same PID.PID130x1fff00Packet Identifier, describing the payload data.Transport scrambling control (TSC)20xc0 '00' = Not scrambled. For DVB-CSA and ATSC DES only:'01' (0x40) = Reserved for future use'10' (0x80) = Scrambled with even key'11' (0xC0) = Scrambled with odd keyAdaptation field control20x3001 – no adaptation field, payload only, 10 – adaptation field only, no payload, 11 – adaptation field followed by payload, 00 – RESERVED for future use Continuity counter40xfSequence number of payload packets (0x00 to 0x0F) within each stream (except PID 8191)Incremented per-PID, only when a payload flag is set.Optional fieldsAdaptation fieldvariablePresent if adaptation field control is 10 or 11. See below for format.Payload datavariablePresent if adaptation field control is 01 or 11. Payload may be PES packets, program specific information (below), or other data.
+ Adaptation field formatNameNumber of bitsBitmaskDescriptionAdaptation field length8 Number of bytes in the adaptation field immediately following this byteDiscontinuity indicator10x80Set if current TS packet is in a discontinuity state with respect to either the continuity counter or the program clock referenceRandom access indicator10x40Set when the stream may be decoded without errors from this pointElementary stream priority indicator10x20Set when this stream should be considered "high priority"PCR flag10x10Set when PCR field is presentOPCR flag10x08Set when OPCR field is presentSplicing point flag10x04Set when splice countdown field is presentTransport private data flag10x02Set when transport private data is presentAdaptation field extension flag10x01Set when adaptation extension data is presentOptional fieldsPCR48 Program clock reference, stored as 33 bits base, 6 bits reserved, 9 bits extension.The value is calculated as base * 300 + extension.OPCR48 Original Program clock reference. Helps when one TS is copied into anotherSplice countdown8 Indicates how many TS packets from this one a splicing point occurs (Two's complement signed; may be negative)Transport private data length8 The length of the following fieldTransport private datavariable Private dataAdaptation extensionvariable See belowStuffing bytesvariableAlways 0xFF
+ Adaptation extension formatNameNumber of bitsBitmaskDescriptionAdaptation extension length80xff00The length of the headerLegal time window (LTW) flag10x0080Piecewise rate flag10x0040Seamless splice flag10x0020Reserved50x001fOptional fieldsLTW flag set (2 bytes)LTW valid flag10x8000LTW offset150x7fffExtra information for rebroadcasters to determine the state of buffers when packets may be missing.Piecewise flag set (3 bytes)Reserved20xc00000Piecewise rate220x3fffffThe rate of the stream, measured in 188-byte packets, to define the end-time of the LTW.Seamless splice flag set (5 bytes)Splice type40xf000000000Indicates the parameters of the H.262 splice.DTS next access unit360x0efffefffeThe 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. +Payload formatNameNumber of bitsBitmaskDescriptionPayload Pointer (optional)80xffPresent 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 PayloadvariableThe content of the payload.
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 will be used to decide how often a particular PID appears in the transport stream.
+ Packet identifiers in use Decimal Hexadecimal Description 00x0000Program association table (PAT) contains a directory listing of all program map tables10x0001Conditional access table (CAT) contains a directory listing of all ITU-T Rec. H.222 entitlement management message streams used by program map tables20x0002Transport stream description table (TSDT) contains descriptors relating to the overall transport stream30x0003IPMP control information table contains a directory listing of all ISO/IEC 14496-13 control streams used by program map tables4–150x0004-0x000FReserved for future use16–310x0010-0x001FUsed by DVB metadata 0x0010: NIT, ST 0x0011: SDT, BAT, ST 0x0012: EIT, ST, CIT 0x0013: RST, ST 0x0014: TDT, TOT, ST 0x0015: network synchronization 0x0016: RNT 0x0017-0x001B: reserved for future use 0x001C: inband signalling 0x001D: measurement 0x001E: DIT 0x001F: SIT32-81860x0020-0x1FFAMay be assigned as needed to program map tables, elementary streams and other data tables81870x1FFBUsed by DigiCipher 2/ATSC MGT metadata8188–81900x1FFC-0x1FFEMay be assigned as needed to program map tables, elementary streams and other data tables81910x1FFFNull Packet (used for fixed bandwidth padding)
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 (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 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 null packets have a payload that is filled with 0xFF, and the receiver is expected to ignore its contents.
M2TS
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, commonly found in HDV 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.
Use in digital video cameras JVC called M2TS "TOD" when used in HDD-based camcorders like GZ-HD7. It is also used to synchronize video streams from several cameras in a multiple-camera setup.
Use in Blu-ray