perf: optimize critical rendering and data processing paths

- Refactor `AmbientBackground` to use `ResizeObserver` instead of polling layout in animation loop.
- Implement async chunking for `ExploreDataService` to prevent main thread blocking during heavy calculations.
- Throttle `UrlHealthController` video probes to a maximum of 3 concurrent requests to prevent resource exhaustion.
- Document optimization tasks in `OPTIMIZATION_TASKS.md`.

Co-authored-by: PR0M3TH3AN <[email protected]>

OPTIMIZATION_TASKS.md

@@ -0,0 +1,50 @@
+# Optimization Task Stubs
+
+The following tasks were identified and implemented to resolve high CPU/GPU usage and potential crashes on the website.
+
+## Completed Tasks
+
+### 1. Optimize Ambient Background Animation
+**Problem:** The `AmbientBackground` controller was calling `resizeCanvas` inside the `requestAnimationFrame` loop. This function accessed `getBoundingClientRect()`, causing synchronous layout thrashing (forced reflow) on every frame, leading to high CPU/GPU usage.
+**Fix:**
+- Refactor `js/ui/ambientBackground.js` to use `ResizeObserver`.
+- Only update canvas dimensions when the element actually resizes.
+- Remove layout reads from the animation loop.
+
+### 2. Async Chunking for Explore Data Service
+**Problem:** `ExploreDataService` performed heavy synchronous iterations over large datasets (Watch History and Video Tags) on the main thread. This could cause the UI to freeze (long tasks) during initialization or updates.
+**Fix:**
+- Refactor `buildWatchHistoryTagCounts` and `buildTagIdf` in `js/services/exploreDataService.js`.
+- Implement processing in chunks (e.g., 500 items).
+- Yield to the main thread using `setTimeout` between chunks to allow user interaction and frame rendering.
+
+### 3. Throttle URL Health Video Probes
+**Problem:** The `UrlHealthController` spawned a `<video>` element for every video card to probe connectivity. When loading a grid of 50+ videos, this caused a storm of simultaneous media decoding requests, leading to resource exhaustion and browser instability.
+**Fix:**
+- Refactor `js/ui/urlHealthController.js`.
+- Implement a concurrency limiter (queue) for `probeUrlWithVideoElement`.
+- Limit active video probes to a maximum of 3 concurrent instances.
+
+## Future Optimization Tasks
+
+### 4. Virtualize Video List Rendering
+**Description:** Implement virtual scrolling (windowing) for the main video grid.
+**Benefit:** Reduces DOM node count and memory usage when displaying thousands of videos.
+**Action:**
+- Create a `VirtualScroller` component.
+- Only render video cards that are currently in the viewport (plus a buffer).
+
+### 5. Move Heavy Computation to Web Worker
+**Description:** Move the tag IDF and Watch History analysis entirely off the main thread.
+**Benefit:** Zero impact on UI responsiveness during data refreshes.
+**Action:**
+- Create `js/workers/exploreData.worker.js`.
+- Move `ExploreDataService` logic into the worker.
+- Use `postMessage` to send video data and receive calculated stats.
+
+### 6. Optimize Image Loading with `loading="lazy"` & `decoding="async"`
+**Description:** Ensure all thumbnails and avatars use modern browser lazy loading.
+**Benefit:** Faster initial page load and lower bandwidth usage.
+**Action:**
+- Audit `VideoCard` and `VideoModal` templates.
+- Ensure `<img>` tags have `loading="lazy"` and `decoding="async"`.

js/services/exploreDataService.js

@@ -6,6 +6,9 @@ import { buildVideoAddressPointer } from "../utils/videoPointer.js";
 const DEFAULT_IDF_REFRESH_INTERVAL_MS = 5 * 60 * 1000;
 const DEFAULT_HISTORY_REFRESH_INTERVAL_MS = 60 * 1000;
 const DEFAULT_REFRESH_DEBOUNCE_MS = 200;
+const YIELD_CHUNK_SIZE = 500;
+
+const yieldToMain = () => new Promise((resolve) => setTimeout(resolve, 0));
 
 function normalizeAddressKey(value) {
   if (typeof value !== "string") {
@@ -99,7 +102,8 @@ export async function buildWatchHistoryTagCounts({
     return counts;
   }
 
-  for (const entry of items) {
+  for (let i = 0; i < items.length; i++) {
+    const entry = items[i];
     const pointer = normalizePointerInput(entry?.pointer || entry);
     let video = entry?.video || entry?.metadata?.video || null;
 
@@ -123,12 +127,16 @@ export async function buildWatchHistoryTagCounts({
     for (const tag of tags) {
       counts.set(tag, (counts.get(tag) || 0) + 1);
     }
+
+    if (i > 0 && i % YIELD_CHUNK_SIZE === 0) {
+      await yieldToMain();
+    }
   }
 
   return counts;
 }
 
-export function buildTagIdf({ videos } = {}) {
+export async function buildTagIdf({ videos } = {}) {
   const idf = new Map();
   const list = Array.isArray(videos) ? videos : [];
   if (!list.length) {
@@ -138,23 +146,31 @@ export function buildTagIdf({ videos } = {}) {
   const docFrequency = new Map();
   const totalDocs = list.length;
 
-  for (const video of list) {
+  for (let i = 0; i < list.length; i++) {
+    const video = list[i];
     const tags = collectVideoTags(video);
-    if (!tags.size) {
-      continue;
+    if (tags.size) {
+      for (const tag of tags) {
+        docFrequency.set(tag, (docFrequency.get(tag) || 0) + 1);
+      }
     }
 
-    for (const tag of tags) {
-      docFrequency.set(tag, (docFrequency.get(tag) || 0) + 1);
+    if (i > 0 && i % YIELD_CHUNK_SIZE === 0) {
+      await yieldToMain();
     }
   }
 
+  let processedCount = 0;
   for (const [tag, df] of docFrequency.entries()) {
     const ratio = (totalDocs + 1) / (df + 1);
     const value = 1 + Math.log(ratio);
     if (Number.isFinite(value) && value > 0) {
       idf.set(tag, value);
     }
+    processedCount++;
+    if (processedCount % YIELD_CHUNK_SIZE === 0) {
+      await yieldToMain();
+    }
   }
 
   return idf;
@@ -310,7 +326,7 @@ export default class ExploreDataService {
     }
   }
 
-  refreshTagIdf({ force = false, videos, reason } = {}) {
+  async refreshTagIdf({ force = false, videos, reason } = {}) {
     const now = Date.now();
     if (!force && this.tagIdfUpdatedAt) {
       const elapsed = now - this.tagIdfUpdatedAt;
@@ -326,7 +342,7 @@ export default class ExploreDataService {
       : [];
 
     try {
-      this.tagIdf = buildTagIdf({ videos: sourceVideos });
+      this.tagIdf = await buildTagIdf({ videos: sourceVideos });
       this.tagIdfUpdatedAt = now;
     } catch (error) {
       if (this.logger?.warn) {

js/ui/ambientBackground.js

@@ -135,7 +135,7 @@ export function attachAmbientBackground(videoElement, canvasElement, options = {
   let destroyed = false;
   let lastTime = 0;
   let tainted = false;
-  let resizeBound = false;
+  let resizeObserver = null;
 
   const clearCanvas = () => {
     if (!canvasElement) {
@@ -152,9 +152,12 @@ export function attachAmbientBackground(videoElement, canvasElement, options = {
       cancelFrame(rafId);
       rafId = 0;
     }
-    if (resizeBound && win) {
+    if (resizeObserver) {
+      resizeObserver.disconnect();
+      resizeObserver = null;
+    }
+    if (win) {
       win.removeEventListener("resize", handleResize);
-      resizeBound = false;
     }
   };
 
@@ -176,7 +179,11 @@ export function attachAmbientBackground(videoElement, canvasElement, options = {
     lastTime = timestamp;
 
     try {
-      const { width, height } = resizeCanvas(canvasElement, videoElement);
+      // Optimization: Rely on ResizeObserver for dimensions.
+      // Do NOT call resizeCanvas() here to avoid layout thrashing.
+      const width = canvasElement.width || 0;
+      const height = canvasElement.height || 0;
+
       if (!width || !height) {
         schedule();
         return;
@@ -203,10 +210,26 @@ export function attachAmbientBackground(videoElement, canvasElement, options = {
     running = true;
     lastTime = 0;
     resizeCanvas(canvasElement, videoElement);
-    if (win && !resizeBound) {
+
+    if (!resizeObserver && win && typeof win.ResizeObserver === "function") {
+      try {
+        resizeObserver = new win.ResizeObserver(() => {
+          if (!destroyed) {
+            resizeCanvas(canvasElement, videoElement);
+          }
+        });
+        const host = canvasElement.parentElement || canvasElement;
+        resizeObserver.observe(host);
+      } catch (err) {
+        if (logger && typeof logger.warn === "function") {
+          logger.warn("[ambientBackground] Failed to initialize ResizeObserver", err);
+        }
+      }
+    } else if (win && !resizeObserver) {
+      // Fallback for browsers without ResizeObserver
       win.addEventListener("resize", handleResize);
-      resizeBound = true;
     }
+
     step();
   };
 

js/ui/urlHealthController.js

@@ -11,6 +11,10 @@ export default class UrlHealthController {
     this.logger = logger;
     this.constants = constants;
     this.callbacks = callbacks;
+
+    this.activeVideoProbes = 0;
+    this.videoProbeQueue = [];
+    this.MAX_CONCURRENT_VIDEO_PROBES = 3;
   }
 
   getUrlHealthPlaceholderMarkup(options = {}) {
@@ -254,67 +258,85 @@ export default class UrlHealthController {
       return { outcome: "error" };
     }
 
-    return new Promise((resolve) => {
-      const video = document.createElement("video");
-      let settled = false;
-      let timeoutId = null;
+    if (this.activeVideoProbes >= this.MAX_CONCURRENT_VIDEO_PROBES) {
+      await new Promise((resolve) => {
+        this.videoProbeQueue.push(resolve);
+      });
+    }
 
-      const cleanup = () => {
-        if (timeoutId) {
-          clearTimeout(timeoutId);
+    this.activeVideoProbes++;
+
+    try {
+      return await new Promise((resolve) => {
+        const video = document.createElement("video");
+        let settled = false;
+        let timeoutId = null;
+
+        const cleanup = () => {
+          if (timeoutId) {
+            clearTimeout(timeoutId);
+          }
+          video.removeEventListener("loadeddata", handleSuccess);
+          video.removeEventListener("canplay", handleSuccess);
+          video.removeEventListener("error", handleError);
+          try {
+            video.pause();
+          } catch (err) {
+            // ignore pause failures
+          }
+          try {
+            video.removeAttribute("src");
+            video.load();
+          } catch (err) {
+            // ignore cleanup failures
+          }
+        };
+
+        const settle = (result) => {
+          if (settled) {
+            return;
+          }
+          settled = true;
+          cleanup();
+          resolve(result);
+        };
+
+        const handleSuccess = () => {
+          settle({ outcome: "ok" });
+        };
+
+        const handleError = () => {
+          settle({ outcome: "error" });
+        };
+
+        if (Number.isFinite(effectiveTimeout) && effectiveTimeout > 0) {
+          timeoutId = setTimeout(() => {
+            settle({ outcome: "timeout" });
+          }, effectiveTimeout);
         }
-        video.removeEventListener("loadeddata", handleSuccess);
-        video.removeEventListener("canplay", handleSuccess);
-        video.removeEventListener("error", handleError);
+
         try {
-          video.pause();
-        } catch (err) {
-          // ignore pause failures
-        }
-        try {
-          video.removeAttribute("src");
+          video.preload = "metadata";
+          video.muted = true;
+          video.playsInline = true;
+          video.addEventListener("loadeddata", handleSuccess, { once: true });
+          video.addEventListener("canplay", handleSuccess, { once: true });
+          video.addEventListener("error", handleError, { once: true });
+          video.src = trimmed;
           video.load();
         } catch (err) {
-          // ignore cleanup failures
+          settle({ outcome: "error", error: err });
         }
-      };
-
-      const settle = (result) => {
-        if (settled) {
-          return;
+      });
+    } finally {
+      this.activeVideoProbes--;
+      if (this.videoProbeQueue.length > 0) {
+        const next = this.videoProbeQueue.shift();
+        if (typeof next === "function") {
+          next();
         }
-        settled = true;
-        cleanup();
-        resolve(result);
-      };
-
-      const handleSuccess = () => {
-        settle({ outcome: "ok" });
-      };
-
-      const handleError = () => {
-        settle({ outcome: "error" });
-      };
-
-      if (Number.isFinite(effectiveTimeout) && effectiveTimeout > 0) {
-        timeoutId = setTimeout(() => {
-          settle({ outcome: "timeout" });
-        }, effectiveTimeout);
       }
-
-      try {
-        video.preload = "metadata";
-        video.muted = true;
-        video.playsInline = true;
-        video.addEventListener("loadeddata", handleSuccess, { once: true });
-        video.addEventListener("canplay", handleSuccess, { once: true });
-        video.addEventListener("error", handleError, { once: true });
-        video.src = trimmed;
-        video.load();
-      } catch (err) {
-        settle({ outcome: "error", error: err });
-      }
-    });
+    }
   }
 
   async probeUrl(url, options = {}) {