MP1 (formally MPEG-1 Audio Layer I or MPEG-2Audio Layer I) is a lossy audio codec and one of three audio formats included in the MPEG-1 standard. For files only containing MP1 audio, the file extension .mp1 is used.
It is a deliberately simplified version of MPEG-1 Audio Layer II, 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 due to wider acceptance of the more complex MPEG-1 Audio Layer II (MP2) and MPEG-1 Audio Layer III (MP3) codecs.
A limited version of MPEG-1 Audio 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.
Specification
MPEG-1 Audio Layer I is defined in ISO/IEC 11172-3, the first version of which was published in 1993.
↑"Philips DCC System Description Draft". Archive.org. Philips Consumer Electronics B.V. September 1994. Retrieved 14 April 2021. The padding bit [...] indicates whether the current frame has a 'dummy' slot