I have some 12 hour long mp3s, each containing a number of stand-alone
items.

I'm looking for a Windows mp3 player where I can make up a playlist or a
library where, for each entry in the list/library, I can specify the mp3
filename, the start point and either the end point or the play length of the
item in that file.

Basically, I'm trying to avoid having to cut the mp3s into bits.

Any suggestions? TIA