You can use either AutoPlaylists or Collections to filter on extension. They can be used for playback and sync.

Hi. I have library entries with BOTH flac and mp3 versions of the same song. Would it be possible to extend the PLAY menu by adding a fourth line to the uppermost options? If would suggest the following:
- Play Next *.[u][i]extension[/i][/u]

The justification would be the ability to play only the selected extension song(s) only without having to manually select each every second (or third) version of an album(s) song. Example - (*.flac). I already sort the selections by filename (to preserve the track order, which usually works). This is minor, but it is a chore to manually click on every other (or third) entry when your artist has a number of albums. I know that workarounds probably exist (virt CD's, etc.), but as everything that is selected to play is usually spur of the moment, so playlists, etc. are not worth the time. Both (or more) versions (flac, mp3, ...) exist to make the transfer of music to external devices faster.

I think this addition to existing user-friendly options would be welcomed.