ATSC: Advanced Television Systems Committee: The committee responsible for the coordination and development of voluntary technical standards for advanced television systems.
Bit Rate: The rate at which the bit stream is delivered from the channel to the input of a decoder.
Bps: Bits per second.
Byte-Aligned: A bit in a coded bit stream is byte-aligned if its position is a multiple of 8-bits from the first bit in the stream.
Communication Channel: A digital medium that transports a digital stream. A communication channel can be uni-directional or bi-directional.
Constant Bit Rate: Operation where the bit rate is constant from start to finish of the bit stream.
CRC: The cyclic redundancy check used to verify the correctness of the data.
Data Access Unit: The portion of a synchronized or synchronous Data Elementary Stream that is associated with a particular MPEG-2 Presentation Time Stamp.
Data Carousel: The scenario of the DSM-CC User-to-Network Download protocol that embodies the cyclic transmission of data.
Data Elementary Stream: The payloads of a series of consecutive MPEG-2 Transport Streams packets referenced by a unique PID value.
Data Element: A self-contained subset of a data elementary stream.
Data Module: An ordered sequence of bytes of a bounded size.
Data Receiver: Any device capable of receiving and consuming data carried on an MPEG-2 Transport Stream.
Data Service: A collection of applications and associated data elementary streams as signaled in a Data Service Table of the Service Description Framework. A data service is characterized by a profile and a level datagram. A datagram is the fundamental protocol data unit in a packet-oriented data delivery protocol. Typically, a datagram is divided into header and data areas, where the header contains full addressing information (source and destination addresses) with each data unit. Datagrams are most often associated with connectionless network and transport layer services.
Data Source: The provider of data that is being inserted into the MPEG-2 Transport Stream.
Decoded Stream: The decoded reconstruction of a compressed bit stream.
Decoder: An embodiment of a decoding process.
Decoding (Process): The process defined in the Digital Television Standard that reads an input coded bit stream and outputs decoded pictures, audio samples, or data objects.
Encoding (Process): A process that reads a stream of input pictures or audio samples and produces a valid coded bit stream as defined in the Digital Television Standard.
Event: A collection of elementary streams with a common time base, an associated start time, and an associated end time. An event is equivalent to the common industry usage of “TV program.”
Forbidden: This term, when used in clauses defining the coded bit stream, indicates that the value shall never be used. This is usually to avoid emulation of start codes.
Huffman Coding: A type of source coding that uses codes of different lengths to represent symbols which have unequal likelihood of occurrence.
Instance: See table instance.
Kbps: 1,000 bits per second.
Latency: The total time when a data object is transmitted in a MPEG-2 transport stream until the time it is fully decoded in the data receiver.
Layer: One of the levels in the data hierarchy of the video and system specification.
Level: The abstracted dimension that is used to refer to the size of the Data Elementary Buffer in the Transport System Target Decoder governing the delivery of Data Access Units of a Data Service.
Logical Channel: See virtual channel.
Maximum Transmission Unit: The largest amount of data that can be transferred in a single unit across a specific physical connection. When using the Internet Protocol, this translates to the largest IP datagram size allowed.
Mbps: 1,000,000 bits per second.
MPEG: Refers to standards developed by the ISO/IEC JTC1/SC29 WG11, Moving Picture
Experts Group. MPEG may also refer to the Group.
MPEG-2: Refers to the collection of ISO/IEC standards 13818-1 through 13818-6.
Multiplexer (Mux): A physical device that is capable of inserting MPEG-2 transport stream packets into and extracting MPEG-2 transport stream packets from an MPEG-2 transport stream.
Multiprotocol Encapsulation: The encapsulation of datagram’s in addressable sections.
Opportunistic Data: Data inserted into the remaining available bandwidth in a given transport stream after all necessary bits have been allocated for video, audio and other services.
Packet: A packet is a set of contiguous bytes consisting of a header followed by its payload.
Packet Identifier (PID): A unique integer value used to associate elementary streams of a program in a single or multi-program transport stream.
Payload: Payload refers to the bytes following the header byte in a packet.
PES Packet Header: The leading fields in a PES packet up to but not including the
PES_packet_data_byte fields where the stream is not a padding stream. In the case of a padding stream, the PES packet header is defined as the leading fields in a PES packet up to but not including the padding_byte fields.
PES Packet: The data structure used to carry elementary stream data. It consists of a packet header followed by PES packet payload.
PES Stream: A continuous sequence of PES packets of one elementary stream with one streamside.
Physical Channel: A generic term to refer to each of the 6-8 MHz frequency bands where television signals are embedded for transmission. Also known as the physical transmission channel (PTC). One analog virtual channel fits in one PTC but multiple digital virtual channels typically coexist in one PTC. The calculations in this document are generally based on the ATSC 6 MHz channel capacity.
Physical Transmission Channel: See physical channel.
Presentation Time-Stamp (PTS): A field that may be present in a PES packet header that indicates the time that a presentation unit is presented in the system target decoder.
Presentation Unit (PU): A decoded audio access unit or a decoded picture.
Program: A collection of program elements. Program elements need not have any defined time base; those that do have a common time base and are intended for synchronized presentation. The term Program is also used in the context of a “television program” such as a scheduled daily news broadcast. In this Standard the term “event” is used for the latter to avoid ambiguity.
Program Clock Reference (PCR): A time stamp in the transport stream from which decoder timing is derived.
Program Element: A generic term for one of the elementary streams or other data streams that may be included in a program. For example: audio, video, data, etc.
Program Specific Information (PSI): PSI consists of normative data which is necessary for the demultiplexing of transport streams and the successful regeneration of programs. ATSC ATSC Data Broadcast Standard (A/90) 26 July 00.
Profile: A defined subset of data delivery characteristics.
PSIP: Program and System Information Protocol is a collection of tables describing virtual channel attributes, event features, and other information.
Reserved: This term, when used in clauses defining the coded bit stream, indicates that the field may be used in the future for Digital Television Standard extensions.
Scrambling: The alteration of the characteristics of a video, audio or coded data stream in order to prevent unauthorized reception of the information in a clear form. This alteration is a specified process under the control of a conditional access system.
Section: A data structure comprising a portion of an ISO/IEC 13818-1  or ISO/IEC 13818-6
-defined table, such as the Program Association Table (PAT), Conditional Access Table (CAT), Program Map Table (PMT) or DSM-CC section. All sections begin with the table_id and end with the CRC_32 or a checksum field, and their starting points within a packet payload are indicated by the pointer_field mechanism defined in .
Service Description Framework: The information conveyed in the program element and providing the Data Service Table and optionally the Network Resource Table of a single data service.
Start Codes: 32-bit codes embedded in the coded bit stream that are unique. They are used for several purposes including identifying some of the layers in the coding syntax. Start codes consist of a 24-bit prefix (0x000001) and an 8-bit stream_id.
STD Input Buffer: A first-in, first-out buffer at the input of a system target decoder for storage of compressed data from elementary streams before decoding.
Stream: An ordered series of bytes. The usual context for the term stream is the series of bytes extracted from Transport Stream packet payloads that have a common unique PID value (e.g., video PES packets or Program Map Table sections).
Stream Data: A stream is a data object which has no specific start or end. The decoding system may need only a small fraction of the total data to activate a given application. An example includes stock ticker services.
Synchronous Data: Data that uses MPEG-2 PCRs and MPEG-2 PTS's with the objective of delivering data units with timing constraints, these data units being processed for presentation and/or display as a standalone stream.
Synchronized Data: Data that uses MPEG-2 PCRs and MPEG-2 PTSs with the objective of matching presentation and/or display of data units with access units of other streams (typically audio and video).
System Target Decoder (STD): A hypothetical reference model of a decoding process used to describe the semantics of the Digital Television Standard multiplexed bit stream.
Table: The collection of re-assembled sections bearing a common version number.
Table Instance: Tables are identified by the table_id field. However, in cases such as the Data
Tap: A reference to a data resource, including but not limited to: a data elementary stream, a data carousel module, or a network resource.
Time-Stamp: A term that indicates the time of a specific action such as the arrival of a byte or the presentation of a presentation unit.
Transport Stream: Refers to the MPEG-2 Transport Stream syntax for the packetization and multiplexing of video, audio, and data signals for digital broadcast systems.
Transport Stream Packet Header: The leading fields in a Transport Stream packet up to and including the continuity counter field.
Virtual Channel: A virtual channel is the designation, usually a number, which is recognized by the user as the single entity that will provide access to an analog TV program or a set of one or more digital elementary streams. It is called “virtual” because its identification (name and number) may be defined independently from its physical location.