MPEG-1 Audio Layer I
Filename extension
Internet media type
audio/mpeg,[1] audio/MPA[2]
Initial releaseDecember 6, 1991; 32 years ago (1991-12-06)[3]
Latest release
ISO/IEC 13818-3:1998
April 1998; 26 years ago (1998-04)
Type of formatLossy audio
Contained byMPEG-ES
StandardISO/IEC 11172-3,[4]
ISO/IEC 13818-3[5]
Open format?Yes
Free format?Expired patents

MPEG-1 Audio Layer I, commonly abbreviated to MP1, is one of three audio formats included in the MPEG-1 standard. It is a deliberately simplified version of MPEG-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 most media players, the codec is considered largely obsolete, and replaced by MP2 or MP3.

For files only containing MP1 audio, the file extension .mp1 is used.

A limited version of MPEG-1 layer I was also used by the Digital 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 simple sub-band coding, using 32 sub-bands.[8]


  1. ^ "The audio/mpeg Media Type - RFC 3003". IETF. November 2000. Retrieved 2009-12-07.
  2. ^ "MIME Type Registration of RTP Payload Formats - RFC 3555". IETF. July 2003. Retrieved 2009-12-07.
  3. ^ Patel K, Smith BC, Rowe LA (1993-09-01). "Performance of a software MPEG video decoder". Proceedings of the first ACM international conference on Multimedia - MULTIMEDIA '93. ACM Multimedia. New York City: Association for Computing Machinery. pp. 75–82. doi:10.1145/166266.166274. ISBN 978-0-89791-596-0. S2CID 3773268. Reference 3 in the paper is to Committee Draft of Standard ISO/IEC 11172, December 6, 1991.
  4. ^ "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". ISO. 1993. Retrieved 2010-07-14.
  5. ^ "ISO/IEC 13818-3:1995 - Information technology -- Generic coding of moving pictures and associated audio information -- Part 3: Audio". ISO. 1995. Retrieved 2010-07-14.
  6. ^ "Philips DCC System Description Draft". Philips Consumer Electronics B.V. September 1994. Retrieved 14 April 2021. The padding bit [...] indicates whether the current frame has a 'dummy' slot
  7. ^ a b "MPEG Audio Frame Header". 2003-08-03. Archived from the original on 2015-02-08. Retrieved 2009-05-29.
  8. ^ "MPEG-1 audio layer 1".