MPEG-1 Audio Layer II

MPEG-1 or MPEG-2 Audio Layer 2
Filename extension .mp2
Internet media type audio/mpeg,[1] audio/MPA[2]
Initial release 1993 (1993)[3]
Type of format Audio compression format, audio file format
Contained by MPEG-ES
Standard ISO/IEC 11172-3,[3]
ISO/IEC 13818-3[4]

MPEG-1 Audio Layer II or MPEG-2 Audio Layer II (MP2, sometimes incorrectly called Musicam or MUSICAM)[5] is a lossy audio compression format defined by ISO/IEC 11172-3 alongside MPEG-1 Audio Layer I and MPEG-1 Audio Layer III (MP3). While MP3 is much more popular for PC and Internet applications, MP2 remains a dominant standard for audio broadcasting.

History of development from MP2 to MP3

MUSICAM

MPEG-1 Audio Layer 2 encoding was derived from the MUSICAM (Masking pattern adapted Universal Subband Integrated Coding And Multiplexing) audio codec, developed by Centre commun d'études de télévision et télécommunications (CCETT), Philips, and the Institut für Rundfunktechnik (IRT) in 1989 as part of the EUREKA 147 pan-European inter-governmental research and development initiative for the development of a system for the broadcasting of audio and data to fixed, portable or mobile receivers (established in 1987).

It began as the Digital Audio Broadcast (DAB) project managed by Egon Meier-Engelen of the Deutsche Forschungs- und Versuchsanstalt für Luft- und Raumfahrt (later on called Deutsches Zentrum für Luft- und Raumfahrt, German Aerospace Center) in Germany. The European Community financed this project, commonly known as EU-147, from 1987 to 1994 as a part of the EUREKA research program.

The Eureka 147 System comprised three main elements: MUSICAM Audio Coding (Masking pattern Universal Sub-band Integrated Coding And Multiplexing), Transmission Coding & Multiplexing and COFDM Modulation.[6]

MUSICAM was one of the few codecs able to achieve high audio quality at bit rates in the range of 64 to 192 kbit/s per monophonic channel. It has been designed to meet the technical requirements of most applications (in the field of broadcasting, telecommunication and recording on digital storage media) — low delay, low complexity, error robustness, short access units, etc.[7][8]

The audio coding algorithm used by the Eureka 147 Digital Audio Broadcasting (DAB) system has been subject to the standardization process within the ISO/Moving Pictures Expert Group (MPEG) in 1989–94.[9][10] MUSICAM audio coding was used as a basis for some coding schemes of MPEG-1 and MPEG-2 Audio.[11] Most key features of MPEG-1 Audio were directly inherited from MUSICAM, including the filter bank, time-domain processing, audio frame sizes, etc. However, improvements were made, and the actual MUSICAM algorithm was not used in the final MPEG-1 Layer II audio standard.

Since the finalisation of MPEG-1 Audio and MPEG-2 Audio (in 1992 and 1994), the original MUSICAM algorithm is not used anymore.[5][12] The name MUSICAM is often mistakenly used when MPEG Audio Layer II is meant. This can lead to some confusion, because the name MUSICAM is trademarked by different companies in different regions of the world.[5][12][13] (Musicam is the name used for MP2 in some specifications for Astra Digital Radio as well as in the BBC's DAB documents.)

The Eureka Project 147 resulted in the publication of European Standard, ETS 300 401 in 1995, for DAB which now has worldwide acceptance. The DAB standard uses the MPEG-1 Audio Layer II (ISO/IEC 11172-3) for 48 kHz sampling frequency and the MPEG-2 Audio Layer II (ISO/IEC 13818-3) for 24 kHz sampling frequency.[14]

MPEG Audio

In the late 1980s, ISO's Moving Picture Experts Group (MPEG) started an effort to standardize digital audio and video encoding, expected to have a wide range of applications in digital radio and TV broadcasting (later DAB, DMB, DVB), and use on CD-ROM (later Video CD).[15] The MUSICAM audio coding was one of 14 proposals for MPEG-1 Audio standard that were submitted to ISO in 1989.[8][11]

The MPEG-1 Audio standard was based on the existing MUSICAM and ASPEC audio formats.[16] The MPEG-1 Audio standard included the three audio "layers" (encoding techniques) now known as Layer I (MP1), Layer II (MP2) and Layer III (MP3). All algorithms for MPEG-1 Audio Layer I, II and III were approved in 1991 as the committee draft of ISO-11172[17][18][19][20] and finalized in 1992[21] as part of MPEG-1, the first standard suite by MPEG, which resulted in the international standard ISO/IEC 11172-3 (a.k.a. MPEG-1 Audio or MPEG-1 Part 3), published in 1993.[3] Further work on MPEG audio[22] was finalized in 1994 as part of the second suite of MPEG standards, MPEG-2, more formally known as international standard ISO/IEC 13818-3 (a.k.a. MPEG-2 Part 3 or backwards compatible MPEG-2 Audio or MPEG-2 Audio BC[23]), originally published in 1995.[4][24] MPEG-2 Part 3 (ISO/IEC 13818-3) defined additional bit rates and sample rates for MPEG-1 Audio Layer I, II and III. The new sampling rates are exactly half that of those originally defined for MPEG-1 Audio. MPEG-2 Part 3 also enhanced MPEG-1's audio by allowing the coding of audio programs with more than two channels, up to 5.1 multichannel.[22]

The Layer III (MP3) component uses a lossy compression algorithm that was designed to greatly reduce the amount of data required to represent an audio recording and sound like a decent reproduction of the original uncompressed audio for most listeners.

Emmy Award in Engineering

CCETT (France), IRT (Germany) and Philips (The Netherlands) won an Emmy Award in Engineering 2000 for development of a digital audio two-channel compression system known as Musicam or MPEG Audio Layer II.[25][26]

Technical specifications

MPEG-1 Audio Layer II is defined in ISO/IEC 11172-3 (MPEG-1 Part 3)

An extension has been provided in MPEG-2 Audio Layer II and is defined in ISO/IEC 13818-3 (MPEG-2 Part 3)[27][28]

The format is based on successive digital frames of 1152 sampling intervals with four possible formats:

Variable bit rate

MPEG audio may have variable bit rate (VBR), but it is not widely supported. Layer II can use a method called bit rate switching. Each frame may be created with a different bit rate.[28][29] According to ISO/IEC 11172-3:1993, Section 2.4.2.3: To provide the smallest possible delay and complexity, the (MPEG audio) decoder is not required to support a continuously variable bit rate when in layer I or II.[30]

How the MP2 format works

Applications of MP2

Part of the DAB digital radio and DVB digital television standards.

Layer II is commonly used within the broadcast industry for distributing live audio over satellite, ISDN and IP Network connections as well as for storage of audio in digital playout systems. An example is NPR's PRSS Content Depot programming distribution system. The Content Depot distributes MPEG-1 L2 audio in a Broadcast Wave File wrapper. MPEG2 with RIFF headers (used in .wav) is specified in the RIFF/WAV standards. As a result, Windows Media Player will directly play Content Depot files, however, less intelligent .wav players often do not. As the encoding and decoding process would have been a significant drain on CPU resources in the first generations of broadcast playout systems, professional broadcast playout systems typically implement the codec in hardware, such as by delegating the task of encoding and decoding to a compatible soundcard rather than the system CPU.

All DVD-Video players in PAL countries contain stereo MP2 decoders, making MP2 a possible competitor to Dolby Digital in these markets. DVD-Video players in NTSC countries are not required to decode MP2 audio, although most do. While some DVD recorders store audio in MP2 and many consumer-authored DVDs use the format, commercial DVDs with MP2 soundtracks are rare.

MPEG-1 layer 2 is the standard audio format used in the Video CD and Super Video CD formats (VCD and SVCD also support variable bit rate and MPEG Multichannel as added by MPEG-2).

MPEG 1 layer 2 is the standard audio format used in the MHP standard for set-top boxes.

MPEG 1 layer 2 is the audio format used in HDV camcorders.

MP2 files are compatible with some Portable audio players.

Naming and extensions

The term MP2 and filename extension .mp2 usually refer MPEG-1 Audio Layer II data, but can also refer to MPEG-2 Audio Layer II, a mostly backwards compatible extension which adds support for multichannel audio, variable bit rate encoding, and additional sampling rates, defined in ISO/IEC 13818-3. The abbreviation MP2 is also sometimes erroneously applied to MPEG-2 video or MPEG-2 AAC audio.

See also

Notes

  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. 1 2 3 "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.
  4. 1 2 "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.
  5. 1 2 3 "MPEG Audio FAQ Version 9". 1998. Retrieved 2010-08-22.
  6. ↑ A J Bower (1998). "Digital Radio — The Eureka 147 DAB System". UK: BBC. Retrieved 2010-08-22.
  7. ↑ "A MUSICAM source codec for digital audio broadcasting and storage". 1991. Retrieved 2010-08-22.
  8. 1 2 "AES E-Library – Musicam Source Coding". 1991. Retrieved 2010-08-22.
  9. ↑ Digital Audio Broadcasting (DAB); DAB to mobile, portable and fixed receivers – Details of 'DE/JTC-DAB' Work Item – ETS 300 401, 1995-02-15, retrieved 2010-08-23
  10. ↑ DAB – Service planning for terrestrial Digital Audio Broadcasting (PDF), 1992, retrieved 2010-08-22
  11. 1 2 "Status report of ISO MPEG – September 1990". 1990. Retrieved 2010-08-22.
  12. 1 2 Telos Systems. "Facts about MPEG compression". Retrieved 2010-08-22.
  13. ↑ MUSICAM USA. "MUSICAM USA Frequently Asked Questions – Isn't MUSICAM simply your implementation of ISO/MPEG Layer 2?". Retrieved 2010-08-23.
  14. ↑ Radio Broadcasting Systems; Digital Audio Broadcasting (DAB) to mobile, portable and fixed receivers – Details of 'REN/JTC-DAB-36' Work Item – EN 300 401, 2006-06-15, retrieved 2010-08-23
  15. ↑ Kurihama 89 press release.
  16. ↑ Digital Video and Audio Broadcasting Technology: A Practical Engineering Guide (Signals and Communication Technology) ISBN 3-540-76357-0 p. 144: "In the year 1988, the MASCAM method was developed at the Institut für Rundfunktechnik (IRT) in Munich in preparation for the digital audio broadcasting (DAB) system. From MASCAM, the MUSICAM (masking pattern universal subband integrated coding and multiplexing) method was developed in 1989 in cooperation with CCETT, Philips and Matsushita."
  17. ↑ ISO (November 1991). "MPEG Press Release, Kurihama, November 1991". ISO. Retrieved 2010-07-17.
  18. ↑ ISO (November 1991). "CD 11172-3 - CODING OF MOVING PICTURES AND ASSOCIATED AUDIO FOR DIGITAL STORAGE MEDIA AT UP TO ABOUT 1.5 MBIT/s Part 3 AUDIO". neuron2.net. Archived from the original (DOC) on June 11, 2010. Retrieved 2010-07-17.
  19. ↑ Kuriham 91 press release.
  20. ↑ Performance of a Software MPEG Video Decoder Article's reference 3 is: 'ISO/IEC JTC/SC29, "Coded Representation of Picture, Audio and Multimedia/Hypermedia Information", Committee Draft of Standard ISO/IEC 11172, December 6, 1991'.
  21. ↑ ISO (1992-11-06). "MPEG Press Release, London, 6 November 1992". chiariglione.org. Retrieved 2010-07-17.
  22. 1 2 "Press Release - Adopted at 22nd WG11 meeting" (Press release). International Organization for Standardization. 1993-04-02. Retrieved 2010-07-18.
  23. ↑ ISO (October 1998). "MPEG Audio FAQ Version 9 - MPEG-1 and MPEG-2 BC". ISO. Retrieved 2009-10-28.
  24. ↑ Brandenburg, Karlheinz; Bosi, Marina (February 1997). "Overview of MPEG Audio: Current and Future Standards for Low-Bit-Rate Audio Coding". Journal of the Audio Engineering Society. 45 (1/2): 4–21. Retrieved 30 June 2008.
  25. ↑ National Academey of Television Arts and Sciences, Outstanding Achievement in Technical/Engineering Development Awards (PDF), retrieved 2010-08-01
  26. ↑ "CCETT - DAB : Digital Audio Broadcasting (archived website)". 2001-02-11. Archived from the original on 2001-02-11. Retrieved 2010-08-01.
  27. ↑ Werner Oomen, Leon van de Kerkhof. "MPEG-2 Audio Layer I/II". chiariglione.org. Retrieved 2009-12-29.
  28. 1 2 Predrag Supurovic (September 1998). "MPEG Audio Frame Header". Retrieved 2009-07-11.
  29. ↑ ISO MPEG Audio Subgroup, MPEG Audio FAQ Version 9, MPEG-1 and MPEG-2 BC, retrieved on 2009-07-11.
  30. ↑ TwoLAME: MPEG Audio Layer II VBR, retrieved on 2009-07-11.

References

External links

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