Elementary stream
Encyclopedia
An elementary stream 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" bitstream
s 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
.
and III
. The sound sample block is encoded within an audio frame:
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:
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.
Encoder
An encoder is a device, circuit, transducer, software program, algorithm or person that converts information from one format or code to another, for the purposes of standardization, speed, secrecy, security, or saving space by shrinking size.-Media:...
. 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" bitstream
Bitstream
A bitstream or bit stream is a time series of bits.A bytestream is a series of bytes, typically of 8 bits each, and can be regarded as a special case of a bitstream....
s 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
Packetized Elementary Stream
Packetized Elementary Stream is a specification in the MPEG-2 Part 1 and ITU-T H.222.0 that defines carrying of elementary streams in packets within MPEG program stream and MPEG transport stream...
.
Header for MPEG-2 video elementary stream
| Field Name | # of bits | Description |
|---|---|---|
| start code | 32 | 0x000001B3 |
| Horizontal Size | 12 | |
| Vertical Size | 12 | |
| Aspect ratio Aspect ratio The aspect ratio of a shape is the ratio of its longer dimension to its shorter dimension. It may be applied to two characteristic dimensions of a three-dimensional shape, such as the ratio of the longest and shortest axis, or for symmetrical objects that are described by just two measurements,... |
4 | |
| Frame rate Frame rate Frame rate is the frequency at which an imaging device produces unique consecutive images called frames. The term applies equally well to computer graphics, video cameras, film cameras, and motion capture systems... code |
4 | |
| Bit rate Bit rate In telecommunications and computing, bit rate is the number of bits that are conveyed or processed per unit of time.... |
18 | Actual bit rate = bit rate * 400, rounded upwards. Use 0x3FFFF for variable bit rate. |
| Marker bit | 1 | Always 1. |
| VBV Video buffering verifier The video buffering verifier is a theoretical MPEG video buffer model used to ensure that an encoded video stream can be correctly buffered and played back at the decoder device.... buf size |
10 | Size of video buffer verifier = 16*1024*vbv buf size |
| constrained parameters flag | 1 | |
| load intra quantizer matrix Quantization (image processing) Quantization, involved in image processing, is a lossy compression technique achieved by compressing a range of values to a single quantum value. When the number of discrete symbols in a given stream is reduced, the stream becomes more compressible. For example, reducing the number of colors... |
1 | If bit set then intra quantizer matrix follows, otherwise use default values. |
| intra quantizer matrix Quantization (image processing) Quantization, involved in image processing, is a lossy compression technique achieved by compressing a range of values to a single quantum value. When the number of discrete symbols in a given stream is reduced, the stream becomes more compressible. For example, reducing the number of colors... |
0 or 64*8 | |
| load non intra quantizer matrix Quantization (image processing) Quantization, involved in image processing, is a lossy compression technique achieved by compressing a range of values to a single quantum value. When the number of discrete symbols in a given stream is reduced, the stream becomes more compressible. For example, reducing the number of colors... |
1 | If bit set then non intra quantizer matrix follows. |
| non intra quantizer matrix Quantization (image processing) Quantization, involved in image processing, is a lossy compression technique achieved by compressing a range of values to a single quantum value. When the number of discrete symbols in a given stream is reduced, the stream becomes more compressible. For example, reducing the number of colors... |
0 or 64*8 |
General layout of MPEG-1 audio elementary stream
The digitized sound signal is divided up into blocks of 384 samples in Layer I and 1152 samples in Layers IIMPEG-1 Audio Layer II
MPEG-1 Audio Layer II or MPEG-2 Audio Layer II is a lossy audio compression format defined by ISO/IEC 11172-3 alongside MPEG-1 Audio Layer I and MPEG-1 Audio Layer III...
and III
MP3
MPEG-1 or MPEG-2 Audio Layer III, more commonly referred to as MP3, is a patented digital audio encoding format using a form of lossy data compression...
. 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
Cyclic redundancy check
A cyclic redundancy check is an error-detecting code commonly used in digital networks and storage devices to detect accidental changes to raw data...
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 Cyclic redundancy check A cyclic redundancy check is an error-detecting code commonly used in digital networks and storage devices to detect accidental changes to raw data... (16bit CRC follows header) '1'=Not Protected |
| bit rate Bit rate In telecommunications and computing, bit rate is the number of bits that are conveyed or processed per unit of time.... 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 Copyright Copyright is a legal concept, enacted by most governments, giving the creator of an original work exclusive rights to it, usually for a limited time... |
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
- MP3MP3MPEG-1 or MPEG-2 Audio Layer III, more commonly referred to as MP3, is a patented digital audio encoding format using a form of lossy data compression...
- Packetized elementary streamPacketized Elementary StreamPacketized Elementary Stream is a specification in the MPEG-2 Part 1 and ITU-T H.222.0 that defines carrying of elementary streams in packets within MPEG program stream and MPEG transport stream...
- MPEG program stream
- MPEG transport stream