frame pacing fix

internal/playback/video_bridge.go

@@ -57,6 +57,19 @@ func (b *VideoBridge) Next(
 	}
 }
 
+// TryNext returns a frame only when a producer is already waiting. It never
+// blocks the caller, allowing UI/render loops to run independently of video
+// frame cadence. A returned frame has the same completion requirements as
+// one returned by Next.
+func (b *VideoBridge) TryNext() (*PendingVideoFrame, bool) {
+	select {
+	case pending := <-b.requests:
+		return pending, true
+	default:
+		return nil, false
+	}
+}
+
 func (f *PendingVideoFrame) Complete(err error) {
 	f.completeOnce.Do(func() {
 		f.result <- err