![]() It lists all programs available in the transport stream. PAT stands for Program Association Table. The MPEG-2 specification does not specify the format of the CAT and NIT. There are 4 PSI tables: Program Association (PAT), Program Map (PMT), Conditional Access (CAT), and Network Information (NIT). Main article: Program Specific Information A single program transport stream is referred to as SPTS. A transport stream with more than one program is referred to as MPTS - Multi Program Transport Stream. It can discard the contents of all other PIDs. A receiver wishing to decode a particular "channel" merely has to decode the payloads of each PID associated with its program. Suppose each channel consists of one video stream, one or two audio streams, and any necessary metadata. For instance, a transport stream used in digital television might contain three programs, to represent three television channels. 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. Transport stream has a concept of programs. In most applications, Time-division multiplexing will be used to decide how often a particular PID appears in the transport stream. A demultiplexer extracts elementary streams from the transport stream in part by looking for packets identified by the same PID. Indicates how many TS packets from this one a splicing point occurs (may be negative)Įach table or elementary stream in a transport stream is identified by a 13-bit packet ID (PID). Set to 1 if the PES packet in this TS packet starts a video/audio sequenceġ means adaptation field does contain a PCR fieldġ means presence of splice countdown field in adaptation fieldġ means presence of private data bytes in adaptation fieldġ means presence of adaptation field extension Set to 1 if a discontinuity occurred in the continuity counter of the TS packet Number of bytes in the adaptation field immediately following this byte The 188-byte packet size was originally chosen for compatibility with ATM systems. ATSC transmission adds 20 bytes of Reed-Solomon forward error correction to create a packet that is 208 bytes long. DVB-ASI uses 204 bytes and ATSC 208 bytes as transport stream packet. Packets are 188 bytes in length, but the communication medium may add some error correction bytes to the packet. The rest of the packet consists of payload. Additional optional transport fields, as signaled in the optional adaptation field, may follow. This is followed by a 4-bit continuity counter. It consists of a sync byte, whose value is 0x47, followed by three one- bit flags and a 13-bit Packet Identifier (PID). Note: the total number of bits above is 32 and is called the transport stream 4-byte prefix.Ī packet is the basic unit of data in a transport stream. The following per DVB spec: '01' = Reserved for future use, '10' = Scrambled with even key, '11' = Scrambled with odd key One means higher priority than other packets with the same PID. Set by demodulator if can't correct errors in the stream ġ means start of PES data or PSI otherwise zero only. Packet Partial Transport Stream Packet Format Name ![]() ![]() Important elements of a transport stream ![]() See Program and System Information Protocol for more information. Encoding block or just block-a DCT encoding block, 8x8 pixelsĪn example of data that is muxed into the transport stream is an electronic program guide.Macroblock-consisting of 6 to 12 DCT blocks.Slice - preventing an error from being propagated through intra prediction.Group of pictures (GOP) - providing random access points.Elementary stream (ES) - audio or video (the below is for video only).An example stream containing video may be processed as follows: Similar to the OSI network protocol stack, a transport stream is processed by the receiver in layers. 3 Modifications of transport stream specification for random-access media (M2TS).2 Important elements of a transport stream. ![]()
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