Download the
Audacity audio editor (unless you have something better), and load the audio file in. Be sure the whole file is visible in the window, and press <Ctrl><A> to Select All. The use the "Effect" menu, and down the list a bit is "Sliding Time Scale / Pitch Shift". If the file is like 18 seconds long, then you would need about a +15% setting to have it play in about 15 seconds. You'll probably have to do some experimenting with it. If it's like 24 seconds long, then the warbling, squirrellie girbels (the real name is "artifact") would really rear their ugly "voice", and it would really sound awful. A couple-three seconds should transition just fine. Don't change the pitch, just shorten the length of time it plays. Audacity doesn't "Save" a wave file. You'll have to "Export" it. The results mostly depend upon how much you have to shorten the file...
