Elementary stream

http://en.wikipedia.org/wiki/Elementary_stream

An elementary stream (ES) as defined by MPEG communication protocol is usually the output of an audio or video encoder. ES contains only one kind of data, e.g. audio, video or closed caption. An elementary stream is often referred to as "elementary", "data", "audio", or "video" bitstreams or streams. The format of the elementary stream depends upon the codec or data carried in the stream, but will often carry a common header when packetized into a packetized elementary stream.

Contents

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• 1 Header for MPEG-2 video elementary stream
• 2 General layout of MPEG-1 audio elementary stream
• 3 See also
• 4 External links

Header for MPEG-2 video elementary stream[edit]

Partial Sequence Header FormatField Name# of bitsDescriptionstart code320x000001B3Horizontal Size12 Vertical Size12 Aspect ratio4 Frame rate code4 Bit rate18Actual bit rate = bit rate * 400, rounded upwards. Use 0x3FFFF for variable bit rate.Marker bit1Always 1.VBV buf size10Size of video buffer verifier = 16*1024*vbv buf sizeconstrained parameters flag1 load intra quantizer matrix1If bit set then intra quantizer matrix follows, otherwise use default values.intra quantizer matrix0 or 64*8 load non intra quantizer matrix1If bit set then non intra quantizer matrix follows.non intra quantizer matrix0 or 64*8 

General layout of MPEG-1 audio elementary stream[edit]

The digitized sound signal is divided up into blocks of 384 samples in Layer I and 1152 samples in Layers II and III. The sound sample block is encoded within an audio frame:

• header
• error check
• audio data
• ancillary data

The header of a frame contains general information such as the MPEG Layer, the sampling frequency, the number of channels, whether the frame is CRC protected, whether the sound is the original:

Field Name# of bitsDescriptionsync word120xFFFID1'1'=mpeg1 '0'=mpeg2layer2'11'=1 '10'=2 '01'=3no protection1'0'=Protected by CRC (16bit CRC follows header)
'1'=Not Protectedbit rate index4 sampling frequency2kHz '00'=44.1 '01'=48 '10'=32padding1 private1 mode2'00'=Stereo '01'=joint stereo '10'=dual channel '11'=single channelmode extension2 copyright10=none 1=yesoriginal or copy10=copy 1=originalemphasis2 

Although most of this information may be the same for all frames, MPEG decided to give each audio frame such a header in order to simplify synchronization and bitstream editing.