Audio metadata storage

I checked through the questions asked on SO on audio metadata, but could not find one which answers my doubt. Where exactly is the metadata of audio files stored, and in what form? Is it in the form of files or in开发者_运维知识库 a database? And where is this database of files stored?

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Thank you Michelle. My basic confusion was whether the metadata is stored as a part of the file or in a separate file which is stored somewhere else in the file system - like inode in case of Unix like systems. ID3 shows that it is stored with the file as a block of bytes after the actual content of the file.

Is this the way of metadata storage for most of the other file types?

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As far as I know, audio file formats :

• May support metadata standards (e.g. ID3v1, ID3v2, APEtag, iXML)

• May also have their own native metadata format (e.g. MP4 boxes / Quicktime atoms, OGG/FLAC/OPUS/Speex/Theora VorbisComment, WMA native metadata, AIFF / AIFC native metadata...)

=> In these two cases, metadata is stored directly into the audio file itself.

HydrogenAudio maintains a field mapping table between the most common formats : http://wiki.hydrogenaud.io/index.php?title=Tag_Mapping

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That being said, many audio players (e.g. iTunes, foobar2000) allow their users to edit any metadata field in any file, regardless of whether said fields are supported or not by the underlying tagging standards (e.g. adding an "Album Artist" field in an S3M file).

In order to do that, these audio players store metadata in their internal database, thus giving the illusion that the audio file has been "enriched" while its actual content remain unchanged.

Another classic use of audio player databases is to store the following fields :

• Rating
• Number of times played
• Last time played

=> In that case, you'll find metadata in the audio player's internal database