Unless you give it such a high priority that it never schedules anything else you're always going to end up with this problem.
If you're doing anything that requires realtime response then it's going to be difficult. It's going to be hard to give emptris/whatever enough CPU time and also allow the player to do the actual MP3 decoding as well.

See, I don't think that's the case. Even when I run with SCHED_FIFO and highest priority, the same problem occurs. The lyrics scroller isn't chewing up tons of CPU, nor is it asking for guarnateed microsecond-level sleep resolution. All I need for this application is to sleep for, say, 15 milliseconds, instead of "somewhere between 15 and 25 milliseconds" which is what this nanosleep bug ends up doing. I don't need exact realtime response, but to ask for 15 ms and get back something that can be 40% higher is far from ideal.