IWBNI jEmplode showed correct total times for playlists. I occasionally make playlists targetted at cassettes (for travelling without the player), and having total time visible in jEmplode before actually uploading would save time tweaking the lengths.

Since this would be a time-consuming calculation if done on all playlists, it probably ought to be a user option. Perhaps a menu item "Calculate playlist times", or an operation on individual playlists "Calculate time for current playlist and its children".

I'm not sure whether it should write the "duration" field when sending to the player. If so, then playlist durations need only be calculated when adding/removing tracks or at user request (for fixing times when emptool or emplode has been used).