If you set "sync playback to display" in XBMC, an inaccurate clock has no
impact on dropped or skipped frames. Suppose you only have a 24Hz mode and play
material which is 23.976. It would slightly speed up playback: every vblank
interval a frame is rendered.
If you observe skipped frames, the render thread may have been blocked too long
or a vertical retrace was missed.