After upgrading from Lightroom 4.x to Lightroom 5.6, I am having problems with slideshows that have audio. I am running on a desktop with W7 SP1 64-bit with PLENTY of memory, disc space, and CPU power. Here's the results of my testing:
I am using a known good .mp3 file that I've used for years on LR3 and LR4, and this .mp3 plays fine in many other programs.
When I set the slide show up and add the audio file in L/R 5.6, it plays fine. I can move around inside of LR5.6, like back to the Library module, and then return to the Slideshow module, and it still works fine.
But if I exit L/R 5.6, and then run it again later, then when I click on the slideshow to play, it starts up and even plays the music for about half a second, and then the whole slideshow hangs... no music, no new slides.
If I then remove (uncheck) the slideshow audio, and retry, the slideshow runs fine (but of course, there's no audio).
If I then re-add the audio file, it also runs fine until I exit and re-enter the L/R program. Then it hangs again.
I've tried other .mp3 files, but all of them produce the same pattern of behavior in L/R 5.6 slide shows, even though they all play fine elsewhere, so I think this must be a L/R issue.