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
Famous quotes containing the words general, elementary and/or stream:
“Every gazette brings accounts of the untutored freaks of the wind,—shipwrecks and hurricanes which the mariner and planter accept as special or general providences; but they touch our consciences, they remind us of our sins. Another deluge would disgrace mankind.”
—Henry David Thoreau (1817–1862)
“As if paralyzed by the national fear of ideas, the democratic distrust of whatever strikes beneath the prevailing platitudes, it evades all resolute and honest dealing with what, after all, must be every healthy literature’s elementary materials.”
—H.L. (Henry Lewis)
“I confess my belief in the common man.... The man who is swimming against the stream knows the strength of it.... The man who is in the melee knows what blows are being struck and what blood is being drawn.”
—Woodrow Wilson (1856–1924)