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How tempo and key values are stored in audio tags.

Some audio formats have standard ways that people have gone about storing extra metadata such as the harmonic key of a song or its average beats per minute. Other formats use non-standard extensions that severely limit compatibility. When possible, tuneXplorer uses standard fields, otherwise, iTunes-compatible extensions.

BPM (beats per minute)

  • In ID3v2 tags, the BPM is stored in the 'TBPM' frame. This is part of the ID3v2.x standard.
  • In Xiph comment tags, the BPM is conventionally stored in a field with the key 'BPM'.
  • In APE metadata tags, the BPM is stored in an atom named 'BPM'.
  • In MP4 tags, the tempo is stored in a 'tmpo' atom. This is part of the MP4 standard.
  • In ASF tags, the tempo is conventionally stored in a field 'WM/BeatsPerMinute'.

Harmonic Key

  • In ID3v2 tags, the initial key of the song is stored in a 'TKEY' frame. This is part of the ID3v2.x standard.
  • In Xiph comment tags, the key is stored in the custom field 'INITIALKEY'.
  • In APE metadata tags, the key is stored in the custom field 'INITIALKEY'.
  • In MP4 tags, the key is stored in the custom field "----:com.apple.iTunes:initialkey".
  • In ASF tags, the key is conventionally stored in a field "WM/InitialKey".

Integration with Other Software

  • Windows Explorer - doesn't support ID3v2.4 tags. Use only ID3v2.3 version if you want to see the changes. Key tags supported only for MP3 and WMA files.
  • iTunes - support only BPM tags. Use "Update common tags" option to save Key values in Comments
  • Serato Scratch Live - reads BPM and Key tags from the 'TBPM' and 'TKEY' frames in ID3v2. Handling of Xiph, APE, ASF and MP4 is unknown.
  • Traktor Pro - reads BPM and Key tags from the 'TBPM' and 'TKEY' frames in ID3v2. Handling of Xiph, APE, ASF and MP4 is unknown.

Remark regarding WAV file metadata

WAV files don't really have a metadata section the same way an MP3 does. However, many applications support ID3v2 tags in RIFF chunks. For better compatibility, consider converting WAV and AIFF files to lossless format, such FLAC or ALAC.