I have probably 80% of my music library with FLAC files, but it is not by artist or anything other than by album. I have ripped all to lossy as well, as many players such as in the car don't cope with e.g. FLAC files, and so need to maintain both sets.

It would be awesome if the library could, rather than having to have the WMA/MP3/M4A files listed completely separately from the FLAC files, understand that there are songs where there is more than one format available and allow playing of the best quality of each individual song within the currently playing list - and especially within playlists.

Currently I have to manually setup the non-FLAC and FLAC (plus some non-FLAC) versions of playlists, which is a painful and error-prone process.

Even if this were just a feature of the playlists management, including for linked playlists, so that:
- if the song was not found with the extension specified in the playlist, it could look for the same song (based on metadata, etc.) with a different extension/file format
- a variant of a playlist can be generated that uses a different base format, so that you could take an existing MP3/WMA/M4A-based playlist and "upgrade" the music to FLAC for any tracks where they had a FLAC version

One way this could work would be to have the option to specific in any playlist the order in which file extensions/formats could be considered - so for the hiDef version of an existing playlist, you could specific that it should override the file format using the rule "FLAC then WMA then M4A then MP3..." or simple "FLAC then Original" whilst, if you had a FLAC-based set of playlists, you would specify overriding the file format with e.g. "WMA then M4A then MP3" to make a playlist for non-lossless devices.

This sort of plays on some of the underlying thinking within the rendering for different devices, but surfaces it for users to be able to manage the playlists and especially music better.