Editing MP3 (section)

=== Metadata ===
{{main|ID3|APEv2 tag}}

A "tag" in an audio file is a section of the file that contains [[metadata]] such as the title, artist, album, track number, or other information about the file's contents. The MP3 standards do not define tag formats for MP3 files, nor is there a standard [[container format]] that would support metadata and obviate the need for tags. However, several ''de facto'' standards for tag formats exist. As of 2010, the most widespread are [[ID3|ID3v1 and ID3v2]], and the more recently introduced [[APEv2 tag|APEv2]]. These tags are normally embedded at the beginning or end of MP3 files, separate from the actual MP3 frame data. MP3 decoders either extract information from the tags or just treat them as ignorable, non-MP3 junk data.

Playing and editing software often contains tag editing functionality, but there are also [[tag editor]] applications dedicated to the purpose. Aside from metadata about the audio content, tags may also be used for [[Digital rights management|DRM]].<ref name="Rae" /> [[ReplayGain]] is a standard for measuring and storing the loudness of an MP3 file ([[audio normalization]]) in its metadata tag, enabling a ReplayGain-compliant player to automatically adjust the overall playback volume for each file. [[MP3Gain]] may be used to reversibly modify files based on ReplayGain measurements so that adjusted playback can be achieved on players without ReplayGain capability.