Generally for iPod you will use a file-based tracksession.  The iPod will fill-out a tracksession with other files in 
the folder you select.  For example, if you create a file-based tracksession the first file in /Music/Songs/All/ the 
iPod will load all other items from the same folder into the playback engine.  It will play the song you've selected 
first, but then it will play another one from that folder.  The typical iPod tracksession is a file-based tracksession 
of only one item--the specific item that the user has selected.

There are some exceptions to this general use.
  1. If you sync the iPod to the library you can use library-based tracksessions.  The same "autofill" of the playback 
engine mentioned above occurs, so you would generally only play one fid from the library and the iPod will carry on 
after that;
  2. if you sync the iPod to the library AND use iPod stalked mode, you build library-based tracksessions with a list of
 the specific fids you want to play.  Stalker mode has the MME specifically stop the iPod after each track has played, 
then the MME tells the iPod which song to play next.  It's not perfect, but it is necessary if you want specific control
 over the playback order;
  3. if you are resuming an iPod's playback using its existing playback engine (for example, when the user first 
connects the device), playback is usually done with the function mme_play_resume_msid().  This function automatically 
creates a library-based tracksession, though that is inconsequential to the caller.

I'm not sure if iPod sync is in MME 1.2.1, and I don't think iPod stalker mode is.  If you need either of these and 
don't have access to these features you'll have to talk to your QNX sales rep about a newer MME version.

-- 
Ryan J. Allen
QNX Software Systems