Here are the characteristics of my perfect digital music file format. Would someone please invent? Note that most of these are not compression type specific. It stands to reason that much of this functionality could be included in new ID3 specs and/or extensions to the MP3 file type.
– Robust metadata, at least equivalent to current ID3 spec plus ability to embed dynamically updatable rating data (good idea, Greer!), links to websites, and machine-readable score data for classical pieces.
– Artwork support for multiple files (images or rich media) including the ability to reference an external file or the embedded artwork of another audio file. For instance, it would save hundreds of MB of file space if you could have a single file on an album contain the artwork for all the tracks on the album.
– Ability to recall point at which the file was last played (bookmarkable), like an m4b file.
– Ability to designate (or not) totally gapless continuous play for a selection of tracks (normally an album).
– File type that is essentially a pointer or shortcut. An application of this would be to allow you to delete two of the three identical versions of, say, How Soon Is Now? because it exists on Meat is Murder, Hatful of Hollow and the Smiths Greatest Hits. The track could live at one place but be included as an alias in the other. When copying the albums with shortcuts the system would offer you the ability to copy the full track or just the pointer. (Would do the same for the externally-referenced artwork in the idea above.)
– Variable compression including lossless. Same file format, just different compression schemes.
– No DRM of any kind.