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 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.
Read more about this topic: Elementary Stream
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