dropped-frame tracke

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
+}