diff --git a/cmd/mxl-player/main.go b/cmd/mxl-player/main.go
index 1142d80..9d7e21d 100644
--- a/cmd/mxl-player/main.go
+++ b/cmd/mxl-player/main.go
@@ -467,7 +467,7 @@ func main() {
 		displayedVideoStride uint32 = placeholderStride
 
 		fps          float64
-		lastIndex    uint64
+		dropTracker  videoDropTracker
 		dropped      uint64
 		droppedTotal uint64
 		frameCount   uint64
@@ -530,6 +530,8 @@ func main() {
 			resized = false
 		}
 		var shownIndex uint64
+		var shownGeneration uint64
+		var shownSource playback.FeedConfig
 		hasFrame := false
 
 		frameCtx, frameCancel := context.WithTimeout(ctx, 100*time.Millisecond)
@@ -555,6 +557,8 @@ func main() {
 			}
 
 			shownIndex = pendingFrame.Frame.Index
+			shownGeneration = pendingFrame.Generation
+			shownSource = pendingFrame.Source
 			displayedVideoWidth = pendingFrame.Frame.Width
 			displayedVideoHeight = pendingFrame.Frame.Height
 			displayedVideoStride = pendingFrame.Frame.Stride
@@ -565,15 +569,14 @@ func main() {
 			panic(frameErr)
 		}
 
+		snapshot, hasSnapshot := player.Controller.Snapshot()
+
 		// stats
 		if hasFrame {
-			if lastIndex != 0 && shownIndex > lastIndex {
-				if g := shownIndex - lastIndex - 1; g > 0 {
-					dropped += g
-					droppedTotal += g
-				}
+			if gap := dropTracker.Observe(shownGeneration, shownSource, shownIndex); gap > 0 {
+				dropped += gap
+				droppedTotal += gap
 			}
-			lastIndex = shownIndex
 			frameCount++
 			if now := time.Now(); now.Sub(lastReport) >= time.Second {
 				dt := now.Sub(lastReport).Seconds()
@@ -588,7 +591,6 @@ func main() {
 		// end of stats
 		if r != nil {
 			gui.BeginFrame(time.Since(lastFrame), int32(r.Extent().Width), int32(r.Extent().Height))
-			snapshot, hasSnapshot := player.Controller.Snapshot()
 			if showStats {
 				cimgui.SetNextWindowPos(cimgui.Vec2{X: 0, Y: 0})
 				cimgui.SetNextWindowSize(cimgui.Vec2{X: 460, Y: 510})
diff --git a/cmd/mxl-player/video_drop_tracker.go b/cmd/mxl-player/video_drop_tracker.go
new file mode 100644
index 0000000..ca5c44e
--- /dev/null
+++ b/cmd/mxl-player/video_drop_tracker.go
@@ -0,0 +1,37 @@
+package main
+
+import "mxl-player/internal/playback"
+
+// videoDropTracker counts gaps only within one playback generation. Frame
+// indices belong to their source and cannot be compared across feed changes.
+type videoDropTracker struct {
+	generation uint64
+	source     playback.FeedConfig
+	lastIndex  uint64
+	hasIndex   bool
+}
+
+func (t *videoDropTracker) Observe(
+	generation uint64,
+	source playback.FeedConfig,
+	index uint64,
+) uint64 {
+	if !t.hasIndex ||
+		generation != t.generation ||
+		!sameVideoSource(source, t.source) ||
+		index <= t.lastIndex {
+		t.generation = generation
+		t.source = source
+		t.lastIndex = index
+		t.hasIndex = true
+		return 0
+	}
+
+	dropped := index - t.lastIndex - 1
+	t.lastIndex = index
+	return dropped
+}
+
+func sameVideoSource(a, b playback.FeedConfig) bool {
+	return a.Domain == b.Domain && a.UUID == b.UUID
+}
diff --git a/cmd/mxl-player/video_drop_tracker_test.go b/cmd/mxl-player/video_drop_tracker_test.go
new file mode 100644
index 0000000..5239f53
--- /dev/null
+++ b/cmd/mxl-player/video_drop_tracker_test.go
@@ -0,0 +1,71 @@
+package main
+
+import (
+	"testing"
+
+	"mxl-player/internal/playback"
+)
+
+func TestVideoDropTracker(t *testing.T) {
+	tests := []struct {
+		name         string
+		observations [][2]uint64
+		want         []uint64
+	}{
+		{
+			name:         "counts gaps within generation",
+			observations: [][2]uint64{{1, 10}, {1, 11}, {1, 15}},
+			want:         []uint64{0, 0, 3},
+		},
+		{
+			name:         "higher index from new generation resets baseline",
+			observations: [][2]uint64{{1, 10}, {2, 1000000}, {2, 1000001}},
+			want:         []uint64{0, 0, 0},
+		},
+		{
+			name:         "lower index from new generation resets baseline",
+			observations: [][2]uint64{{1, 100}, {2, 5}, {2, 7}},
+			want:         []uint64{0, 0, 1},
+		},
+		{
+			name:         "index restart within generation resets baseline",
+			observations: [][2]uint64{{1, 100}, {1, 0}, {1, 1}},
+			want:         []uint64{0, 0, 0},
+		},
+		{
+			name:         "zero is a valid first index",
+			observations: [][2]uint64{{1, 0}, {1, 2}},
+			want:         []uint64{0, 1},
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			var tracker videoDropTracker
+			source := playback.FeedConfig{Domain: "/mxl", UUID: "video"}
+			for index, observation := range test.observations {
+				got := tracker.Observe(observation[0], source, observation[1])
+				if got != test.want[index] {
+					t.Fatalf("Observe(%d, %d) = %d, want %d",
+						observation[0], observation[1], got, test.want[index])
+				}
+			}
+		})
+	}
+}
+
+func TestVideoDropTrackerResetsWhenSourceChanges(t *testing.T) {
+	var tracker videoDropTracker
+	first := playback.FeedConfig{Domain: "/mxl", UUID: "first"}
+	second := playback.FeedConfig{Domain: "/mxl", UUID: "second"}
+
+	if got := tracker.Observe(1, first, 10); got != 0 {
+		t.Fatalf("first Observe() = %d, want 0", got)
+	}
+	if got := tracker.Observe(1, second, 1000000); got != 0 {
+		t.Fatalf("source-changing Observe() = %d, want 0", got)
+	}
+	if got := tracker.Observe(1, second, 1000002); got != 1 {
+		t.Fatalf("same-source Observe() = %d, want 1", got)
+	}
+}
diff --git a/flow-def/video-4k.json b/flow-def/video-4k.json
new file mode 100644
index 0000000..e850f18
--- /dev/null
+++ b/flow-def/video-4k.json
@@ -0,0 +1,41 @@
+{
+  "description": "sample for mxl reader go player",
+  "id": "5fbec3b1-1b0f-417d-9059-8b94a47197ed",
+  "tags": {
+    "urn:x-nmos:tag:grouphint/v1.0": [
+      "mxl-gst-testsrc pattern"
+    ]
+  },
+  "format": "urn:x-nmos:format:video",
+  "label": "SMPTE bars test video",
+  "parents": [],
+  "media_type": "video/v210",
+  "grain_rate": {
+    "numerator": 25,
+    "denominator": 1
+  },
+  "frame_width": 1920,
+  "frame_height": 1080,
+  "interlace_mode": "progressive",
+  "colorspace": "BT709",
+  "components": [
+    {
+      "name": "Y",
+      "width": 1920,
+      "height": 1080,
+      "bit_depth": 10
+    },
+    {
+      "name": "Cb",
+      "width": 960,
+      "height": 1080,
+      "bit_depth": 10
+    },
+    {
+      "name": "Cr",
+      "width": 960,
+      "height": 1080,
+      "bit_depth": 10
+    }
+  ]
+}
diff --git a/imgui.ini b/imgui.ini
index bc38a87..d88865f 100644
--- a/imgui.ini
+++ b/imgui.ini
@@ -4,12 +4,11 @@ Size=400,400
 Collapsed=0
 
 [Window][Settings & Info]
-Pos=1220,0
-Size=700,1080
+Pos=580,0
+Size=700,720
 Collapsed=0
 
 [Window][Stats]
-Pos=0,0
 Size=460,510
 Collapsed=0
 
diff --git a/internal/playback/sync_attempt.go b/internal/playback/sync_attempt.go
index 995fc67..e36b8b5 100644
--- a/internal/playback/sync_attempt.go
+++ b/internal/playback/sync_attempt.go
@@ -14,6 +14,7 @@ func runSyncAttempt(
 	videoConfig FeedConfig,
 	audioConfig FeedConfig,
 ) (resultErr error) {
+	videoCtx := withVideoSource(ctx, videoConfig)
 	reader, err := factory.OpenSync(
 		ctx,
 		videoConfig,
@@ -39,7 +40,7 @@ func runSyncAttempt(
 			return fmt.Errorf("read sync group: %w", err)
 		}
 
-		if err := videoSink.ConsumeVideo(ctx, frame.Video); err != nil {
+		if err := videoSink.ConsumeVideo(videoCtx, frame.Video); err != nil {
 			if ctx.Err() != nil {
 				return ctx.Err()
 			}
diff --git a/internal/playback/video.go b/internal/playback/video.go
index 98271ee..382be1d 100644
--- a/internal/playback/video.go
+++ b/internal/playback/video.go
@@ -2,6 +2,17 @@ package playback
 
 import "context"
 
+type videoSourceContextKey struct{}
+
+func withVideoSource(ctx context.Context, source FeedConfig) context.Context {
+	return context.WithValue(ctx, videoSourceContextKey{}, source)
+}
+
+func videoSourceFromContext(ctx context.Context) FeedConfig {
+	source, _ := ctx.Value(videoSourceContextKey{}).(FeedConfig)
+	return source
+}
+
 // VideoFrame contains metadata and borrowed source payload.
 //
 // Payload is valid only until the next VideoReader.ReadVideo call or until the
diff --git a/internal/playback/video_attempt.go b/internal/playback/video_attempt.go
index 798f3c3..bdd4ee2 100644
--- a/internal/playback/video_attempt.go
+++ b/internal/playback/video_attempt.go
@@ -24,6 +24,7 @@ func runVideoAttempt(
 	sink VideoSink,
 	config FeedConfig,
 ) (resultErr error) {
+	ctx = withVideoSource(ctx, config)
 	reader, err := factory.OpenVideo(ctx, config)
 	if err != nil {
 		return fmt.Errorf("open video: %w", err)
diff --git a/internal/playback/video_bridge.go b/internal/playback/video_bridge.go
index fb394d5..aa971e6 100644
--- a/internal/playback/video_bridge.go
+++ b/internal/playback/video_bridge.go
@@ -6,7 +6,9 @@ import (
 )
 
 type PendingVideoFrame struct {
-	Frame VideoFrame
+	Frame      VideoFrame
+	Generation uint64
+	Source     FeedConfig
 
 	completeOnce sync.Once
 	result       chan error
@@ -27,8 +29,10 @@ func (b *VideoBridge) ConsumeVideo(
 	frame VideoFrame,
 ) error {
 	pending := &PendingVideoFrame{
-		Frame:  frame,
-		result: make(chan error, 1),
+		Frame:      frame,
+		Generation: generationFromContext(ctx),
+		Source:     videoSourceFromContext(ctx),
+		result:     make(chan error, 1),
 	}
 
 	select {
diff --git a/internal/playback/video_bridge_test.go b/internal/playback/video_bridge_test.go
index 8205b9e..d66a424 100644
--- a/internal/playback/video_bridge_test.go
+++ b/internal/playback/video_bridge_test.go
@@ -21,8 +21,10 @@ func TestVideoBridgeDeliversFrameAndCompletionResult(t *testing.T) {
 	}
 	consumeResult := make(chan error, 1)
 
+	wantSource := FeedConfig{Domain: "/video", UUID: "video", Active: true}
 	go func() {
-		consumeResult <- bridge.ConsumeVideo(context.Background(), wantFrame)
+		ctx := withGeneration(context.Background(), 17)
+		consumeResult <- bridge.ConsumeVideo(withVideoSource(ctx, wantSource), wantFrame)
 	}()
 
 	ctx, cancel := context.WithTimeout(context.Background(), videoBridgeTestTimeout)
@@ -34,6 +36,12 @@ func TestVideoBridgeDeliversFrameAndCompletionResult(t *testing.T) {
 	if pending.Frame.Index != wantFrame.Index {
 		t.Fatalf("Next() frame index = %d, want %d", pending.Frame.Index, wantFrame.Index)
 	}
+	if pending.Generation != 17 {
+		t.Fatalf("Next() generation = %d, want 17", pending.Generation)
+	}
+	if pending.Source != wantSource {
+		t.Fatalf("Next() source = %#v, want %#v", pending.Source, wantSource)
+	}
 	if &pending.Frame.Payload[0] != &wantFrame.Payload[0] {
 		t.Fatal("Next() copied the borrowed payload")
 	}
diff --git a/playlists/sample-list.json b/playlists/sample-list.json
index 51c60e5..ffce9b2 100644
--- a/playlists/sample-list.json
+++ b/playlists/sample-list.json
@@ -15,6 +15,19 @@
       "sync": true,
       "duration": "10s"
     },
+    {
+      "name": "fail",
+      "video": {
+        "domain": "/dev/shm/mxl",
+        "uuid": "6fbec3b1-1b0f-417d-9059-8b94a47197ed"
+      },
+      "audio": {
+        "domain": "/dev/shm/mxl",
+        "uuid": "6fbec3b1-1b0f-417d-9059-8b94a47197ec"
+      },
+      "sync": true,
+      "duration": "10s"
+    },
     {
       "name": "F1 Highlights",
       "video": {