[refactor] share mobile controller protocol and video timing

libs/controller/include/mobile_video_timing.h

@@ -0,0 +1,27 @@
+/*
+ * @Author: DI JUNKUN
+ * @Date: 2026-10-02
+ * Copyright (c) 2026 by DI JUNKUN, All Rights Reserved.
+ */
+
+#ifndef _MOBILE_VIDEO_TIMING_H_
+#define _MOBILE_VIDEO_TIMING_H_
+
+#include <cstdint>
+
+namespace crossdesk::mobile_controller {
+inline double VideoLatencyMilliseconds(uint64_t captured_us,
+                                       uint64_t received_us,
+                                       int64_t submitted_us) {
+  // MiniRTC calibrates capture time when the frame is reassembled. Validate
+  // that mapping at reception, not after decoding/Surface waits: a real local
+  // backlog over five seconds must remain visible in the latency measurement.
+  if (!captured_us || received_us < captured_us || submitted_us <= 0 ||
+      received_us > static_cast<uint64_t>(submitted_us) ||
+      received_us - captured_us > 5'000'000)
+    return -1;
+  return (static_cast<uint64_t>(submitted_us) - captured_us) / 1000.0;
+}
+}  // namespace crossdesk::mobile_controller
+
+#endif