Frame Pacing and V-Sync: Why Correct Emulator Timing Is More Than Average FPS
How source refresh rates, audio clocks, host displays, queues, and synchronization strategies create smooth motion—or periodic stutter and latency.
An emulator can report 60 frames per second and still look uneven. Frame pacing describes when frames appear. A source console may run at a fractional or region-specific refresh rate that does not divide evenly into a 60 Hz desktop mode. The mismatch eventually forces a repeated or dropped host frame.
Multiple clocks compete
The emulated CPU/video clock, audio sample clock, host compositor, GPU queue, and monitor refresh all advance independently. Synchronizing video perfectly may require slight audio resampling. Synchronizing audio exactly may allow a video correction. Unbounded queues hide short stalls but add input latency.
V-sync and variable refresh
V-sync prevents visible tearing by presenting at display boundaries, but a missed boundary can delay a frame. Variable-refresh displays can follow a source rate within their supported range and reduce cadence mismatch. They do not fix an emulator that produces frames irregularly or a shader pipeline that compiles mid-game.
Measure, then choose
Use frame-time graphs rather than an FPS average. Confirm the core’s reported refresh, desktop mode, fullscreen/compositor behavior, buffering, and audio resampling. The right policy depends on whether accuracy, lowest latency, stable audio, recording, or netplay is the priority. No single “sync” checkbox optimizes all five.
Sources: Libretro audio/video synchronization documentation, Dolphin performance guide