What is MPEG transport stream?

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

Transport Stream is specified in MPEG-2 Part 1, Systems. Transport stream specifies a container format encapsulating packetized elementary streams (video, audio and metadata such as subtitles and closed captioning) with error correction and stream synchronization features for maintaining transmission integrity when the signal is degraded.

Transport streams differ from program streams in several 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. Transport streams may also carry multiple programs. Multiple MPEG programs are combined and sent to a transmitting antenna. In the U.S. broadcast digital TV system, a receiver then decodes the TS and displays it. In most other parts of the world, transmission would be accomplished by one or more variants of the modular DVB system.

Each program is described by a Program Map Table (PMT) which has a unique PID (packet identifier), 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, representing three television channels. Each channel may consist of one video stream, one or two audio streams and any necessary metadata. A receiver wishing to decode a particular channel decodes the payloads of each PID associated with its program. It can discard the contents of all other PIDs.

Transport Stream was originally designed for broadcast but was later adapted for use with digital video cameras, recorders and players by adding a 4-byte timecode (TC) to standard 188-byte packets. This is what is informally called M2TS stream. The timecode allows quick access to any part of the stream either from a media player or from a non-linear video editing system (useful for quick reference and transcription of filmed material). It is also used to synchronize video streams from several cameras in a multi-camera shoot.

Filename extension .m2ts is used on Blu-ray Disc Video for files which contain an incompatible BDAV MPEG-2 transport stream. Blu-ray Disc employs the MPEG-2 transport stream recording method. That 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.