| MPEG-1 Audio Layer I | |
|---|---|
| Filename extension | .mp1 |
| Internet media type | |
| Initial release | December 6, 1991; 33 years ago (1991-12-06)[3] |
| Latest release | ISO/IEC 13818-3:1998 April 1998; 27 years ago (1998-04) |
| Type of format | Lossyaudio |
| Contained by | MPEG-ES |
| Standard | ISO/IEC 11172-3,[4] ISO/IEC 13818-3[5] |
| Open format? | Yes |
| Free format? | Expired patents |
| Website | http://mpeg.chiariglione.org/standards/mpeg-1/audio |
MPEG-1 Audio Layer I, commonly abbreviated toMP1, is alossy audio codec and one of three audio formats included in theMPEG-1 standard. For files only containing MP1 audio, the file extension.mp1 is used.
It is a deliberately simplified version ofMPEG-1 Audio Layer II (MP2), created for applications where lower compression efficiency could be tolerated in return for a less complex algorithm that could be executed with simpler hardware requirements. While supported by mostmedia players, the codec is considered largely obsolete due to wider acceptance of the more complexMPEG-1 Audio Layer II andLayer III (MP3) MPEG-1 codecs.
A limited version of MPEG-1 layer I was also used by theDigital Compact Cassette format, in the form of the PASC (Precision Adaptive Subband Coding) audio compression codec. The bit rate of PASC was fixed at 384 kilobits per second, and when encoding audio at a sample frequency of 44.1 kHz, PASC regards the padding slots as 'dummy'[6] and sets them to zero, whereas the ISO/IEC 11172-3 standard uses them to store data.
MPEG-1 Layer I is defined in ISO/IEC 11172-3, the first version of which was published in 1993.
An extension has been provided in MPEG-2 Layer I and is defined in ISO/IEC 13818-3, which first version was published in 1995.
MP1 uses a comparatively simplesub-band coding, using 32 sub-bands.[8]
The padding bit [...] indicates whether the current frame has a 'dummy' slot