diff --git a/tests/utils/video-timestamps.test.mjs b/tests/utils/video-timestamps.test.mjs
new file mode 100644
index 00000000..ef787c5a
--- /dev/null
+++ b/tests/utils/video-timestamps.test.mjs
@@ -0,0 +1,239 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+
+import {
+  getVideoRootIdentifier,
+  applyRootTimestampToVideosMap,
+  syncActiveVideoRootTimestamp,
+} from "../../js/utils/videoTimestamps.js";
+
+test("getVideoRootIdentifier returns videoRootId if present", () => {
+  const video = { videoRootId: "root-123", id: "event-456" };
+  assert.equal(getVideoRootIdentifier(video), "root-123");
+});
+
+test("getVideoRootIdentifier returns id if videoRootId is missing", () => {
+  const video = { id: "event-456" };
+  assert.equal(getVideoRootIdentifier(video), "event-456");
+});
+
+test("getVideoRootIdentifier returns empty string if no identifier is found", () => {
+  assert.equal(getVideoRootIdentifier({}), "");
+  assert.equal(getVideoRootIdentifier(null), "");
+  assert.equal(getVideoRootIdentifier(undefined), "");
+  assert.equal(getVideoRootIdentifier(42), "");
+});
+
+test("applyRootTimestampToVideosMap updates videos with same root ID", () => {
+  const video1 = { id: "v1", videoRootId: "root1" };
+  const video2 = { id: "v2", videoRootId: "root1" };
+  const video3 = { id: "v3", videoRootId: "root2" };
+
+  const videosMap = new Map([
+    ["v1", video1],
+    ["v2", video2],
+    ["v3", video3],
+  ]);
+
+  applyRootTimestampToVideosMap({
+    videosMap,
+    video: video1,
+    rootId: "root1",
+    timestamp: 1000,
+  });
+
+  assert.equal(video1.rootCreatedAt, 1000);
+  assert.equal(video2.rootCreatedAt, 1000);
+  assert.equal(video3.rootCreatedAt, undefined);
+});
+
+test("applyRootTimestampToVideosMap skips updates if rootId is empty", () => {
+  const video1 = { id: "v1", videoRootId: "root1" };
+  const video2 = { id: "v2", videoRootId: "root1" };
+  const videosMap = new Map([
+    ["v1", video1],
+    ["v2", video2],
+  ]);
+
+  applyRootTimestampToVideosMap({
+    videosMap,
+    video: video1,
+    rootId: "",
+    timestamp: 1000,
+  });
+
+  assert.equal(video1.rootCreatedAt, 1000); // Updated because of video.id match
+  assert.equal(video2.rootCreatedAt, undefined); // Skipped because rootId is empty
+});
+
+test("applyRootTimestampToVideosMap handles non-object values in map", () => {
+  const video1 = { id: "v1", videoRootId: "root1" };
+  const videosMap = new Map([
+    ["v1", video1],
+    ["v2", null],
+    ["v3", "not an object"],
+  ]);
+
+  applyRootTimestampToVideosMap({
+    videosMap,
+    video: video1,
+    rootId: "root1",
+    timestamp: 1000,
+  });
+
+  assert.equal(video1.rootCreatedAt, 1000);
+});
+
+test("applyRootTimestampToVideosMap handles missing videosMap safely", () => {
+  // Should not throw
+  applyRootTimestampToVideosMap({
+    videosMap: null,
+    video: { id: "v1" },
+    rootId: "root1",
+    timestamp: 1000,
+  });
+});
+
+test("syncActiveVideoRootTimestamp updates active video state with lastEditedAt", () => {
+  const activeVideo = {
+    id: "v1",
+    videoRootId: "root1",
+    created_at: 500,
+    lastEditedAt: 600.5,
+  };
+
+  let updateCalled = false;
+  const videoModal = {
+    updateMetadata: ({ timestamps, tags }) => {
+      updateCalled = true;
+      assert.equal(timestamps.postedAt, 2000);
+      assert.equal(timestamps.editedAt, 600); // Floor of 600.5
+    },
+  };
+
+  const buildModalTimestampPayload = ({ postedAt, editedAt }) => ({
+    postedAt,
+    editedAt,
+  });
+
+  const result = syncActiveVideoRootTimestamp({
+    activeVideo,
+    rootId: "root1",
+    timestamp: 2000.7,
+    buildModalTimestampPayload,
+    videoModal,
+  });
+
+  assert.strictEqual(result, true);
+  assert.equal(activeVideo.rootCreatedAt, 2000);
+  assert.ok(Array.isArray(activeVideo.displayTags));
+  assert.strictEqual(updateCalled, true);
+});
+
+test("syncActiveVideoRootTimestamp fallback to created_at if lastEditedAt missing", () => {
+  const activeVideo = {
+    id: "v1",
+    videoRootId: "root1",
+    created_at: 500.9,
+  };
+
+  let updateCalled = false;
+  const videoModal = {
+    updateMetadata: ({ timestamps }) => {
+      updateCalled = true;
+      assert.equal(timestamps.editedAt, 500);
+    },
+  };
+
+  syncActiveVideoRootTimestamp({
+    activeVideo,
+    timestamp: 2000,
+    buildModalTimestampPayload: (p) => p,
+    videoModal,
+  });
+
+  assert.strictEqual(updateCalled, true);
+});
+
+test("syncActiveVideoRootTimestamp handles missing timestamps in activeVideo", () => {
+  const activeVideo = {
+    id: "v1",
+    videoRootId: "root1",
+  };
+
+  let updateCalled = false;
+  const videoModal = {
+    updateMetadata: ({ timestamps }) => {
+      updateCalled = true;
+      assert.strictEqual(timestamps.editedAt, null);
+    },
+  };
+
+  syncActiveVideoRootTimestamp({
+    activeVideo,
+    timestamp: 2000,
+    buildModalTimestampPayload: (p) => p,
+    videoModal,
+  });
+
+  assert.strictEqual(updateCalled, true);
+});
+
+test("syncActiveVideoRootTimestamp handles missing videoModal or payload builder", () => {
+  const activeVideo = {
+    id: "v1",
+    videoRootId: "root1",
+  };
+
+  // Should not throw
+  const result = syncActiveVideoRootTimestamp({
+    activeVideo,
+    timestamp: 2000,
+  });
+
+  assert.strictEqual(result, true);
+  assert.equal(activeVideo.rootCreatedAt, 2000);
+});
+
+test("syncActiveVideoRootTimestamp returns false for invalid conditions", () => {
+  const activeVideo = { id: "v1", videoRootId: "root1" };
+
+  // Invalid timestamp
+  assert.strictEqual(
+    syncActiveVideoRootTimestamp({ activeVideo, timestamp: "invalid" }),
+    false,
+  );
+  assert.strictEqual(
+    syncActiveVideoRootTimestamp({ activeVideo, timestamp: NaN }),
+    false,
+  );
+
+  // Missing activeVideo
+  assert.strictEqual(
+    syncActiveVideoRootTimestamp({ activeVideo: null, timestamp: 1000 }),
+    false,
+  );
+
+  // ID mismatch
+  assert.strictEqual(
+    syncActiveVideoRootTimestamp({
+      activeVideo,
+      rootId: "different-root",
+      timestamp: 1000,
+    }),
+    false,
+  );
+
+  // Missing root identifier in activeVideo
+  assert.strictEqual(
+    syncActiveVideoRootTimestamp({ activeVideo: {}, timestamp: 1000 }),
+    false,
+  );
+
+  // Redundant update
+  activeVideo.rootCreatedAt = 1000;
+  assert.strictEqual(
+    syncActiveVideoRootTimestamp({ activeVideo, timestamp: 1000 }),
+    false,
+  );
+});