perf(visualizer): write bar data at ~10fps

Each Solid setBarData costs a renderer diff pass. Cava already
smooths (noise reduction + peak release), so 3 of every 4 frames now
update only the pipeline; the UI signal writes at >=95ms intervals.

src/stores/visualizer.ts

@@ -344,6 +344,7 @@ function createVisualizerStore(): VisualizerStore {
 
 	// ── Render loop (called at ~30fps) ─────────────────────────────────
 
+	let lastBarWriteAt = 0;
 	const renderFrame = () => {
 		if (!cava?.isReady || !sampleBuffer || !pcm) return;
 
@@ -374,11 +375,17 @@ function createVisualizerStore(): VisualizerStore {
 		const count = pcm.readWindow(sampleBuffer, target);
 		// Never feed a partial FFT window to cava.
 		if (count < sampleBuffer.length) return;
-
 		const output = cava.execute(sampleBuffer);
 
+		// Write the UI signal at ~10fps, not 30: cava already smooths
+		// (noise reduction + peak release), and each Solid write costs a
+		// renderer diff pass. 3 of every 4 frames update only the pipeline.
+		const nowMs = performance.now();
+		if (nowMs - lastBarWriteAt >= 95) {
+			lastBarWriteAt = nowMs;
 			// Normalize against the running peak and copy to a new array
 			setBarData(scaler(output));
+		}
 		// Fresh frames only count once the position clock has MOVED from
 		// the resume point: while the player is still re-buffering after a
 		// long pause, the cache serves the same window and the spinner must

tests/visualizer-throttle.test.ts

@@ -0,0 +1,41 @@
+/** bars signal writes are throttled to ~10fps; the render loop still runs 30fps. */
+import { test, expect } from "bun:test"
+import { join } from "path"
+import { tmpdir } from "os"
+
+process.env.XDG_CONFIG_HOME = join(tmpdir(), `podtui-th-${process.pid}`)
+process.env.XDG_DATA_HOME = join(tmpdir(), `podtui-th-data-${process.pid}`)
+process.env.PODTUI_AUDIO_BACKEND = "none"
+
+const { useVisualizer } = await import("../src/stores/visualizer")
+const { setCurrentEpisode, setIsPlaying, setPosition } = await import("../src/utils/audio-signals")
+import type { Episode } from "../src/types/episode"
+
+const wavPath = "/tmp/podtui-pause-cycle.wav"
+const skip = !(Bun.which("ffmpeg") && Bun.file(wavPath).exists())
+
+test.skipIf(skip)("barData updates at ~10fps while the loop runs at 30fps", async () => {
+  const viz = useVisualizer()
+  viz.setBarCount(64)
+  viz.setFocused(true)
+  setCurrentEpisode({ audioUrl: wavPath } as unknown as Episode)
+  setIsPlaying(true)
+  setPosition(5)
+  for (let i = 0; i < 200 && !(viz.barData().length > 0); i++) await Bun.sleep(25)
+
+  let writes = 0
+  let prev = viz.barData()
+  // count distinct array references the signal produced over 1s
+  const check = setInterval(() => {
+    const cur = viz.barData()
+    if (cur !== prev) {
+      writes++
+      prev = cur
+    }
+  }, 16)
+  await Bun.sleep(1000)
+  clearInterval(check)
+  console.log(`barData writes in 1s: ${writes} (30fps loop would be ~15-20 distinct seen at 16ms sampling)`)
+  expect(writes).toBeGreaterThan(3)
+  expect(writes).toBeLessThanOrEqual(14)
+}, 30_000)