Transport stream: Béda antarrépisi

'''Transport streamstréam''' ('''TS''', '''TP''', or '''MPEG-TS''') nyaetanyaéta hiji [[protokol komunikasi]] keur [[Audio digital|audio]], [[Video digital|video]], jeung [[Program and System Information Protocol|data]] nu ditetepkeun dina [[MPEG-2]] BageanBagéan 1, Systems (standar [[International Organization for Standardization|ISO]]/[[International Electrotechnical Commission|IEC]] 13818-1 [http://web.archive.org/web/20061113181708/http://neuron2.net/library/mpeg2/iso13818-1.pdf]). Tujuan rancangannana nyaetanyaéta keur ngidinan [[multipleksing]] videovidéo jeung audio digital sarta keur [[Audio video sync|nyinkronisasi kaluaran]]. Transport streamstréam nawarkeun fitur keur [[deteksi jeung koreksi kasalahan|ngoreksi kasalahan]] pikeun transportasi ngaliwatan media nu henteu pati dipercaya, sarta dipakedipaké dina aplikasi siaran saperti [[DVB]] jeung [[standar ATSC|ATSC]]. Transport streamstréam beda jeung [[program stream]], nu dirancang keur media nu bisa dipercaya kaws [[DVD]].

Sarua jeung [[OSI_modelOSI model#Description_of_OSI_layersDescription of OSI layers|OSI network]] [[protocol stack]], hiji transport streamstréam diproses ku panarima mangrupa lapisan-lapisan. Hiji streamstréam conto nu ngandung videovidéo bisa diproses kawas kieu:

#[[Elementary stream]] (ES) — audio atawa videovidéo (the below is for videovidéo only)

An example of data that is [[Multiplexer|muxed]] into the transport streamstréam is an [[electronic program guide]]. See [[Program and System Information Protocol]] for more information.

A packet is the basic unit of data in a transport streamstréam. It consists of a [[syncword|sync byte]], whose value is 0x47, followed by three one-[[bit]] flags and a 13-bit PID. This is followed by a 4-bit continuity counter. Additional optional transport fields, as signaled in the optional adaptation field, may follow. The rest of the packet consists of payload. Packets are 188 bytes in length <ref>

, but the communication medium may add some error correction bytes to the packet. DVb-ASI uses 204 bytes and ATSC 208 bytes as transport streamstréam packet. (DVB t=8 and ATSC t=10 i.e. extra bytes = 2*t). ATSC transmission adds 20 bytes of [[Reed-Solomon]] [[forward error correction]] to createcréate a packet that is 208 bytes long [http://broadcastengineering.com/infrastructure/Atsc-transmission-digital-20050620/]. The 188-byte packet size was originally chosen for compatibility with [[Asynchronous Transfer Mode|ATM systems]][http://www.chiariglione.org/mpeg/faq/mp2-sys/mp2-sys.htm#mp2-12] [[http://www.tek.com/site/ps/0,,21-14851-SPECS_EN,00.html]] .

|+ Partial Transport StreamStréam Packet Format

|Set by [[demodulator]] if can't correct errors in the streamstréam [http://www.coolstf.com/tsreader/support.html]

|Payload Unit Start Indicator||1||1 meansméans start of [[Packetized Elementary Stream|PES]] data or [[Program Specific Information|PSI]] otherwise zero only .

|Transport Priority||1||One meansméans higher priority than other packets with the same PID.

|Scrambling control||2|| '00' = Not scrambled. &nbsp; The following per [[DVB]] spec <ref> [http://web.archive.org/web/20031006195927/http://www.bjpace.com.cn/data/tec/tec-DVB/DVB%20BlueBooks%20Standards/Specifications%20and%20Standards/conditional%20access/dvb-csa/A007.pdf DVB scrambling control bits defined. Page 6]</ref>: &nbsp; '01' = Reserved for future use, &nbsp; '10' = Scrambled with even key, &nbsp; '11' = Scrambled with odd key

|Adaptation field exist||1||1 meansméans presence of the adaptation field

|Payload data exist||1||1 meansméans presence of data

| || ||Note: the total number of bits above is 32 and is called the transport streamstréam 4-byte prefix.

|Random Access indicator||1||Set to 1 if the PES packet in this TS packet starts a videovidéo/audio sequence

|PCR flag||1||1 meansméans adaptation field does contain a PCR field

|Splicing point flag||1||1 meansméans presence of splice countdown field in adaptation field

|Transport private data flag||1||1 meansméans presence of private data bytes in adaptation field

|Adaptation field extension flag||1||1 meansméans presence of adaptation field extension

Eachéach table or elementary streamstréam in a transport streamstréam is identified by a 13-bit PID. A [[Inverse multiplexer|demultiplexer]] extracts elementary streamsstréams from the transport streamstréam 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 appearsappéars in the transport streamstréam.

Transport streamstréam has a concept of programs. A single program is described by a Program Map Table (PMT) which has a unique PID, and the elementary streamsstréams associated with that program have PIDs listed in the PMT. For instance, a transport streamstréam used in digital television might contain three programs, to represent three television channels. Suppose eachéach channel consists of one videovidéo streamstréam, one or two audio streamsstréams, and any necessary metadata. A [[ATSC tuner|receiver]] wishing to decode a particular "channel" merely has to decode the payloads of eachéach PID associated with its program. It can discard the contents of all other PIDs.

PAT stands for Program Association Table. The PAT lists PIDs for all PMTs in the streamstréam. TS Packets containing PAT information always have PID 0x0.

Program Map Tables, or PMTs, contain information about programs. For eachéach program, there is a PMT, with the PMT for eachéach program appearingappéaring on its own PID. The PMTs describe which PIDs contain data relevant to the program. PMTs also provide metadata about the streamsstréams in their constituent PIDs. For example, if a program contains an [[MPEG-2]] videovidéo streamstréam, the PMT will list this PID, describe it as a videovidéo streamstréam, and provide the type of videovidéo that it contains (in this case, MPEG-2). The PMT may also contain additional descriptors providing data about its constituent streamsstréams.

To assist the decoder in presenting programs on time, at the right speed, and with synchronization, programs usually periodically provide a ''Program Clock Reference'', or PCR, on one of the PIDs in the program. This is also known as the master clock. Timing in MPEG2 references this clock, for example the presentation time stamp (PTS) is relative to the PCR. The first 33 bits is based on a 90kHz90&nbsp;kHz clock, incremented for eachéach [[Hertz]] or cycle. The 9 bit extension is based on a 27MHz27&nbsp;MHz clock.

Some transmission schemes, such as those in [[ATSC Standards|ATSC]] and [[DVB]], impose strict constant bitrate requirements on the transport streamstréam. In order to ensure that the streamstréam maintains a constant bitrate, a [[Multiplexer]] may need to insert some additional packets. The PID 0x1FFF is reserved for this purpose. The payload of null packets may not contain any data at all, and the receiver is expected to ignore its contents.

*[[HDV]] jeung [[AVCHD]], nu duanan nerapkeun streamstréam TS kana data nu dipaketisasi

[[CategoryKategori:ATSC]]

[[CategoryKategori:MPEG]]