From Wikipedia, the free encyclopedia
An
elementary stream
(
ES
) as defined by the
MPEG
communication protocol is usually the output of an
audio encoder
or
video encoder
. An 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
.
Partial Sequence Header Format
Field Name
|
# of bits
|
Description
|
start code
|
32
|
0x000001B3
|
Horizontal Size
|
12
|
|
Vertical Size
|
12
|
|
Aspect ratio
|
4
|
|
Frame rate
code
|
4
|
|
Bit rate
|
18
|
Actual bit rate = bit rate * 400, rounded upwards. Use 0x3FFFF for variable bit rate.
|
Marker bit
|
1
|
Always 1.
|
VBV
buf size
|
10
|
Size of video buffer verifier = 16*1024*vbv buf size
|
constrained parameters flag
|
1
|
|
load intra
quantizer matrix
|
1
|
If bit set then intra quantizer matrix follows, otherwise use default values.
|
intra
quantizer matrix
|
0 or 64*8
|
|
load non intra
quantizer matrix
|
1
|
If bit set then non intra quantizer matrix follows.
|
non intra
quantizer matrix
|
0 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 bits
|
Description
|
sync word
|
12
|
0xFFF
|
ID
|
1
|
'1'=mpeg1 '0'=mpeg2
|
layer
|
2
|
'11'=1 '10'=2 '01'=3
|
no protection
|
1
|
'0'=Protected by
CRC
(16bit CRC follows header)
'1'=Not Protected
|
bit rate
index
|
4
|
|
sampling frequency
|
2
|
kHz '00'=44.1 '01'=48 '10'=32
|
padding
|
1
|
|
private
|
1
|
|
mode
|
2
|
'00'=Stereo '01'=joint stereo '10'=dual channel '11'=single channel
|
mode extension
|
2
|
|
copyright
|
1
|
0=none 1=yes
|
original or copy
|
1
|
0=copy 1=original
|
emphasis
|
2
|
|
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.
See also
[
edit
]
External links
[
edit
]
- ISO/IEC 11172-3:1993
: Information technology -- Coding of moving pictures and associated audio for digital storage media at up to about 1,5 Mbit/s -- Part 3: Audio