Packetized elementary stream

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Packetized Elementary Stream (PES) is a specification in the MPEG-2 Part 1 (Systems) (ISO/IEC 13818-1) and ITU-T H.222.0 [1] [2] that defines carrying of elementary streams (usually the output of an audio or video encoder) in packets within MPEG program streams and MPEG transport streams. [3] The elementary stream is packetized by encapsulating sequential data bytes from the elementary stream inside PES packet headers.

Contents

A typical method of transmitting elementary stream data from a video or audio encoder is to first create PES packets from the elementary stream data and then to encapsulate these PES packets inside Transport Stream (TS) packets or Program Stream (PS) packets. The TS packets can then be multiplexed and transmitted using broadcasting techniques, such as those used in an ATSC and DVB.

Transport Streams and Program Streams are each logically constructed from PES packets. PES packets shall be used to convert between Transport Streams and Program Streams. In some cases the PES packets need not be modified when performing such conversions. PES packets may be much larger than the size of a Transport Stream packet. [3]

PES packet header

NameSizeDescription
Packet start code prefix3 bytes0x000001
Stream id1 byteExamples: Audio streams (0xC0-0xDF), Video streams (0xE0-0xEF) [4] [5]
Note: The above 4 bytes is called the 32 bit start code.
PES Packet length2 bytesSpecifies the number of bytes remaining in the packet after this field. Can be zero. If the PES packet length is set to zero, the PES packet can be of any length. A value of zero for the PES packet length can be used only when the PES packet payload is a video elementary stream. [6]
Optional PES headervariable length (length >= 3)not present in case of Padding stream & Private stream 2 (navigation data)
DataSee elementary stream. In the case of private streams the first byte of the payload is the sub-stream number.

Optional PES header

NameNumber of BitsDescription
Marker bits210 binary or 0x2 hex
Scrambling control200 implies not scrambled
Priority1
Data alignment indicator11 indicates that the PES packet header is immediately followed by the video start code or audio syncword
Copyright11 implies copyrighted
Original or Copy11 implies original
PTS DTS indicator211 = both present, 01 is forbidden, 10 = only PTS, 00 = no PTS or DTS
ESCR flag1
ES rate flag1
DSM trick mode flag1
Additional copy info flag1
CRC flag1
extension flag1
PES header length8gives the length of the remainder of the PES header in bytes
Optional fieldsvariable lengthpresence is determined by flag bits above
Stuffing Bytesvariable length0xff


While above flags indicate that values are appended into variable length optional fields, they are not just simply written out. For example, PTS (and DTS) is expanded from 33 bits to 5 bytes (40 bits). If only PTS is present, this is done by catenating 0010b, most significant 3 bits from PTS, 1, following next 15 bits, 1, rest 15 bits and 1. If both PTS and DTS are present the same is done, but first 4 bits before start of PTS bits are 0011b (and not 0010b) and first 4 bits before start of DTS bits are 0001b. Other appended bytes have similar but different encoding.

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References

  1. ↑ ITU-T (November 2014). "H.222.0 Summary" . Retrieved 2015-11-17.
  2. ↑ ITU-T. "H.222.0 : Information technology - Generic coding of moving pictures and associated audio information: Systems" . Retrieved 2010-06-03.
  3. 1 2 "ISO/IEC 13818-1 — Information technology — Generic coding of moving pictures and associated audio information: Systems" (PDF) (second ed.). 2000-12-01. Retrieved 2009-07-25.
  4. ↑ "ETSI TS 101 154 - V1.9.1 - Digital Video Broadcasting (DVB); Specification for the use of Video and Audio Coding in Broadcasting Applications based on the MPEG-2 Transport Stream" (PDF). ETSI. September 2009.
  5. ↑ EP 1827030,"Method and apparatus for changing codec to reproduce video and/or audio data streams encoded by different codecs within a channel"
  6. ↑ "A guide to digital terrestrial television broadcasting in the VHF/UHF bands". 15 January 1996. sec. 4.4.
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