frame pacing fix

cmd/mxl-player/frame_pacing.go

@@ -0,0 +1,24 @@
+package main
+
+import "time"
+
+const guiFrameInterval = time.Second / 60
+
+// videoPollInterval bounds GUI latency when no video producer is waiting.
+// It is not a video-rate cap: Next returns immediately whenever a frame
+// arrives, including for sources faster than this interval.
+const videoPollInterval = 8 * time.Millisecond
+
+func remainingFrameTime(start, now time.Time, interval time.Duration) time.Duration {
+	remaining := interval - now.Sub(start)
+	if remaining < 0 {
+		return 0
+	}
+	return remaining
+}
+
+func paceFrame(start time.Time) {
+	if remaining := remainingFrameTime(start, time.Now(), guiFrameInterval); remaining > 0 {
+		time.Sleep(remaining)
+	}
+}

cmd/mxl-player/frame_pacing_test.go

@@ -0,0 +1,29 @@
+package main
+
+import (
+	"testing"
+	"time"
+)
+
+func TestRemainingFrameTime(t *testing.T) {
+	start := time.Date(2026, time.September, 2, 0, 0, 0, 0, time.UTC)
+	interval := 16 * time.Millisecond
+	tests := []struct {
+		name    string
+		elapsed time.Duration
+		want    time.Duration
+	}{
+		{name: "no work", want: interval},
+		{name: "partial budget", elapsed: 5 * time.Millisecond, want: 11 * time.Millisecond},
+		{name: "exact budget", elapsed: interval},
+		{name: "over budget", elapsed: 20 * time.Millisecond},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			got := remainingFrameTime(start, start.Add(test.elapsed), interval)
+			if got != test.want {
+				t.Fatalf("remainingFrameTime() = %v, want %v", got, test.want)
+			}
+		})
+	}
+}

cmd/mxl-player/main.go

@@ -532,6 +532,7 @@ func main() {
 			if err := r.RecreateSwapchain(); err != nil {
 				if errors.Is(err, renderer.ErrMinimized) {
 					resized = true
+					paceFrame(frameStart)
 					continue
 				}
 				panic(err)
@@ -543,7 +544,7 @@ func main() {
 		var shownSource playback.FeedConfig
 		hasFrame := false
 
-		frameCtx, frameCancel := context.WithTimeout(ctx, 100*time.Millisecond)
+		frameCtx, frameCancel := context.WithTimeout(ctx, videoPollInterval)
 		pendingFrame, frameErr := videoBridge.Next(frameCtx)
 		frameCancel()
 
@@ -1094,6 +1095,7 @@ func main() {
 				if rerr := r.RecreateSwapchain(); rerr != nil {
 					if errors.Is(rerr, renderer.ErrMinimized) {
 						resized = true
+						paceFrame(frameStart)
 						continue
 					}
 					panic(rerr)