Editing MP3 (section)

=== Further versions ===

Further work on MPEG audio<ref name="sydney1993" /> 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 backward compatible ''MPEG-2 Audio'' or ''MPEG-2 Audio BC''<ref name="mpeg-audio-faq-bc" />), originally published in 1995.<ref name="13818-3" /><ref name="Brandenburg1997" /> MPEG-2 Part 3 (ISO/IEC 13818-3) defined 42 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 in MPEG-1 Audio. This reduction in sampling rates serves to cut the available frequency fidelity in half while likewise cutting the bit rate by 50%. 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.<ref name="sydney1993" /> An MP3 coded with MPEG-2 results in half of the bandwidth reproduction of MPEG-1 appropriate for piano and singing.

A third generation of "MP3" style data streams (files) extended the ''MPEG-2'' ideas and implementation but was named ''MPEG-2.5'' audio since MPEG-3 already had a different meaning. This extension was developed at Fraunhofer IIS, the registered patent holder of MP3, by reducing the frame sync field in the MP3 header from 12 to 11 bits. As in the transition from MPEG-1 to MPEG-2, MPEG-2.5 adds additional sampling rates exactly half of those available using MPEG-2. It thus widens the scope of MP3 to include human speech and other applications yet requires only 25% of the bandwidth (frequency reproduction) possible using MPEG-1 sampling rates. While not an ISO-recognized standard, MPEG-2.5 is widely supported by both inexpensive Chinese and brand-name digital audio players as well as computer software-based MP3 encoders ([[LAME]]), decoders (FFmpeg) and players (MPC) adding {{math|3 × 8 {{=}} 24}} additional MP3 frame types. Each generation of MP3 thus supports 3 sampling rates exactly half that of the previous generation for a total of 9 varieties of MP3 format files. The sample rate comparison table between MPEG-1, 2, and 2.5 is given later in the article.<ref name="MPEG-2.5" /><ref name="MPEG-2.5-2" /> MPEG-2.5 is supported by LAME (since 2000), Media Player Classic (MPC), iTunes, and FFmpeg.

MPEG-2.5 was not developed by MPEG (see above) and was never approved as an international standard. MPEG-2.5 is thus an unofficial or proprietary extension to the MP3 format. It is nonetheless ubiquitous and especially advantageous for low-bit-rate human speech applications.

{| class="wikitable sortable"
|+MPEG Audio Layer III versions
|-
! Version
! International Standard{{ref label|mp3standard|*|}}
! First edition public release date
! Latest edition public release date
|-
| MPEG-1 Audio Layer III
| [http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=22412 ISO/IEC 11172-3] {{Webarchive|url=https://web.archive.org/web/20120528230220/http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=22412 |date=28 May 2012 }} (MPEG-1 Part 3)<ref name="11172-3" /><ref name="neuron2-cd-1991" />
| 1993
|
|-
| MPEG-2 Audio Layer III
| [http://www.iso.org/iso/iso_catalogue/catalogue_ics/catalogue_detail_ics.htm?csnumber=26797 ISO/IEC 13818-3] {{Webarchive|url=https://web.archive.org/web/20110511043216/http://www.iso.org/iso/iso_catalogue/catalogue_ics/catalogue_detail_ics.htm?csnumber=26797 |date=11 May 2011 }} (MPEG-2 Part 3)<ref name="13818-3" /><ref name="mp3tech-iso13818-3" />
| 1995
| 1998
|-
| MPEG-2.5 Audio Layer III
| nonstandard, Fraunhofer proprietary<ref name="MPEG-2.5" /><ref name="MPEG-2.5-2" />
|2000
|2008
|}
{{refbegin}}
{{note label|mp3standard|*|}}The ISO standard ISO/IEC 11172-3 (a.k.a. MPEG-1 Audio) defined three formats: the MPEG-1 Audio Layer I, Layer II and Layer III. The ISO standard ISO/IEC 13818-3 (a.k.a. MPEG-2 Audio) defined an extended version of MPEG-1 Audio: MPEG-2 Audio Layer I, Layer II, and Layer III. MPEG-2 Audio (MPEG-2 Part 3) should not be confused with MPEG-2 AAC (MPEG-2 Part 7&nbsp;– ISO/IEC 13818-7).<ref name="mpeg-audio-faq-bc" />
{{refend}}

LAME is the most advanced MP3 encoder.{{Citation needed|date=August 2021|reason=Bold claims require verifiable citations}} LAME includes a [[variable bit rate]] (VBR) encoding which uses a quality parameter rather than a bit rate goal. Later versions (2008+) support an ''n.nnn'' quality goal which automatically selects MPEG-2 or MPEG-2.5 sampling rates as appropriate for human speech recordings that need only 5512&nbsp;Hz bandwidth resolution.