diff --git a/docs/VISUAL_FEATURE_COVERAGE.md b/docs/VISUAL_FEATURE_COVERAGE.md
index ef59741..def0003 100644
--- a/docs/VISUAL_FEATURE_COVERAGE.md
+++ b/docs/VISUAL_FEATURE_COVERAGE.md
@@ -60,11 +60,15 @@ What moved to **covered** in the second public-product pass:
   `progressivePreview` selector, **By speed** + **By object** color modes, the parametric fixture,
   and nav links to the model / model-viewer / 2D / CNC-validation / headless-still pages.
 
+**Animations wired up** (WebM, via the harness `encodeWebm` → `image2pipe`/mjpeg → VP8; embedded as
+`<video autoplay loop muted playsinline>`): `scrub-sweep.webm` (segment scrub drawing the toolpath)
+and `layer-buildup.webm` (layer-range sweep — the progressive reveal), in the feature gallery and the
+workers concept page.
+
 Still on the **to-capture** list (honest remainder — recorded, not forgotten):
 
-- `needs animation`: segment/time **scrub**, **progressive / held reveal**, interaction-aware
-  quality, user-scrub-wins — temporal, so a GIF/short clip beats a still (harness has the ffmpeg
-  path via `lib/browser.mjs`; not yet wired into shots).
+- `needs animation`: **time scrub**, interaction-aware quality, user-scrub-wins, and the *actual*
+  load-time progressive/`hold` reveal (the layer-buildup clip stands in for it today).
 - `needs comparison`: **object-aware framing** (whole-job vs model-aware), **fresh vs stale**
   progress, **render scope** (plate/object subset before/after).
 - `needs screenshot`: **diagnostics panel** in-context, **transparent-background capture** over a
@@ -79,7 +83,7 @@ them up rather than rediscovering them.
 | Capability | User-facing | Demo | Media | README | Pages gallery | Manual/pkg | Status |
 |---|:---:|:---:|:---:|:---:|:---:|:---:|---|
 | Layer-range clipping | ✅ | ✅ | `layer-clip-benchy` | ✅ | gallery | recipes | needs better coverage — show the range control + resulting cut |
-| Segment scrub | ✅ | ✅ | — | — | gallery | recipes | needs animation — scrub is temporal |
+| Segment scrub | ✅ | ✅ | `scrub-sweep.webm` | — | gallery | recipes | covered — scrub-sweep animation in the gallery |
 | Time scrub + print-time estimate (slicer vs kinematic provenance) | ✅ | ✅ | — | mention | gallery | concept-progress-motion | needs animation + needs better coverage (provenance label) |
 | Travel-move toggle | ✅ | ✅ | (in others) | ✅ | gallery | recipes | covered |
 | Wipe-move toggle | ✅ | ✅ | — | mention | gallery | — | needs screenshot |
@@ -119,8 +123,8 @@ them up rather than rediscovering them.
 | Line geometry | ✅ | ✅ | `render-lines` | mention | gallery | concept-workers | covered (tubes-vs-lines pair in gallery + concept) |
 | Canvas 2D fallback (no WebGL/Three) | ✅ | 2d page | `canvas-2d-fallback` | ✅ | gallery | concept-workers | covered |
 | Quality modes (full/adaptive/fast) | ✅ | partial | — | mention | gallery | concept-workers | needs demo exposure |
-| Progressive preview (`auto`/`lines`) | ✅ | ✅ (selector) | — | ✅ | gallery | concept-workers | demo + docs covered; animation pending |
-| Held / single clean reveal (`hold`) | ✅ | ✅ (selector) | — | ✅ | gallery | concept-workers | demo + docs covered; animation pending |
+| Progressive preview (`auto`/`lines`) | ✅ | ✅ (selector) | `layer-buildup.webm` | ✅ | gallery | concept-workers | demo + docs + build-up animation; true load-time capture still pending |
+| Held / single clean reveal (`hold`) | ✅ | ✅ (selector) | `layer-buildup.webm` | ✅ | gallery | concept-workers | demo + docs + build-up animation (stand-in); true load-time capture pending |
 | Renderer build stages (`stage` event) | ✅ | ❌ | — | ✅ (prose) | gallery | concept-workers | needs animation |
 | Interaction-aware quality | ✅ | ❌ | — | ✅ (prose) | gallery | concept-workers | needs animation |
 | Disclosed decimation / degradation | ✅ | ✅ (disclosure) | — | ✅ (prose) | gallery | concept-workers | needs screenshot (disclosure text) |
diff --git a/docs/manual/concept-workers.md b/docs/manual/concept-workers.md
index c8e578c..0082767 100644
--- a/docs/manual/concept-workers.md
+++ b/docs/manual/concept-workers.md
@@ -18,6 +18,8 @@ Input is **streamed** into the parser, and the renderer can append geometry as i
 large print shows a growing preview (time-to-first-paint) rather than a spinner until the whole file
 is parsed. The session reports progress as it goes.
 
+<p><video autoplay loop muted playsinline width="640" poster="https://chestnutlabs.github.io/gcode-preview/media/viewer-benchy-tubes.png" style="max-width:100%;border-radius:8px;border:1px solid var(--color-accent)"><source src="https://chestnutlabs.github.io/gcode-preview/media/layer-buildup.webm" type="video/webm"></video></p>
+
 The **`progressivePreview`** prop chooses how that stream is presented (3D):
 
 - **`'lines'`** (default) — show the growing line preview as it parses, then swap in the final build.
diff --git a/docs/manual/feature-gallery.md b/docs/manual/feature-gallery.md
index e7554aa..f35ebdf 100644
--- a/docs/manual/feature-gallery.md
+++ b/docs/manual/feature-gallery.md
@@ -25,6 +25,11 @@ The core job: turn a sliced file into an interactive picture of the actual moves
 | ![Calicat lower layers with retraction and de-retraction markers pinned on the path](../media/retraction-markers.png) | ![The calicat as flat single-pixel toolpath lines](../media/render-lines.png) |
 | **Retraction & de-retraction markers.** Toggle markers for retractions, wipes, travel, and seams. | **Line geometry.** Flat one-pixel paths — lighter for very large files or low-GPU devices. |
 
+<p><video autoplay loop muted playsinline width="720" poster="https://chestnutlabs.github.io/gcode-preview/media/viewer-benchy-tubes.png" style="max-width:100%;border-radius:8px;border:1px solid var(--gp-border)"><source src="https://chestnutlabs.github.io/gcode-preview/media/scrub-sweep.webm" type="video/webm"></video></p>
+
+*Segment scrub sweeping the draw-range through 3DBenchy — the toolpath drawing itself in exact print
+order. Scrubbing is a draw-range trim, so it stays smooth even on large models.*
+
 Also here: **segment scrub** (step move-by-move), **time scrub** with an honest print-time estimate
 (labeled *slicer estimate* vs *kinematic approximation*), and **source-line ↔ segment mapping** — click
 a move to find its byte in the file, and back. See [recipes](recipes.md).
@@ -63,6 +68,11 @@ incoming telemetry; file-identity mismatches are detected and disclosed. See
 | ![The calicat as lit 3D tubes](../media/render-tubes.png) | ![A single layer drawn by the Canvas 2D renderer, no WebGL](../media/canvas-2d-fallback.png) |
 | **Tubes vs lines.** Automatic quality selection, or force either. | **Canvas 2D fallback.** A flat layer view with **no WebGL and no Three.js** — the 2D bundle never ships Three. |
 
+<p><video autoplay loop muted playsinline width="720" poster="https://chestnutlabs.github.io/gcode-preview/media/viewer-benchy-tubes.png" style="max-width:100%;border-radius:8px;border:1px solid var(--gp-border)"><source src="https://chestnutlabs.github.io/gcode-preview/media/layer-buildup.webm" type="video/webm"></video></p>
+
+*Raising the top layer builds the model bottom to top — the same draw-range mechanism, and the visual
+of a progressive reveal.*
+
 Underneath: **quality modes** (full / adaptive / fast), **interaction-aware quality** (drop detail
 while orbiting, restore on settle), a **parallel geometry worker pool** (byte-identical tubes off the
 main thread, degrading pool → serial → lines, all disclosed), **progressive preview** with a **single
diff --git a/docs/media/layer-buildup.webm b/docs/media/layer-buildup.webm
new file mode 100644
index 0000000..4f1ad4d
Binary files /dev/null and b/docs/media/layer-buildup.webm differ
diff --git a/docs/media/scrub-sweep.webm b/docs/media/scrub-sweep.webm
new file mode 100644
index 0000000..139039f
Binary files /dev/null and b/docs/media/scrub-sweep.webm differ
diff --git a/tools/screenshots/README.md b/tools/screenshots/README.md
index 3d6882b..a0fcb72 100644
--- a/tools/screenshots/README.md
+++ b/tools/screenshots/README.md
@@ -96,8 +96,18 @@ Keep framing, viewport, and filenames stable when adding shots so the set reads
 
 ## Animation (temporal captures)
 
-For features where the interaction *is* the point (scrub, progressive reveal), the harness can
-capture a frame sequence and encode it with the Playwright-bundled ffmpeg (auto-located; override
-with `FFMPEG_PATH`). See `lib/browser.mjs` `resolveFfmpeg()`. Reach for animation only when a static
-frame genuinely can't carry the feature — a single well-composed frame or a before/after pair is
-usually clearer and cheaper.
+For features where the interaction *is* the point (scrub, progressive reveal), a shot with
+`"output": "webm"` and an `"anim"` spec sweeps a temporal control across frames and encodes a small,
+looping, muted **WebM** — embedded on the docs site as `<video autoplay loop muted playsinline>`.
+
+```json
+{ "name": "scrub-sweep", "output": "webm",
+  "anim": { "kind": "scrub", "frames": 48, "fps": 16, "holdFrames": 10 } }
+```
+
+`kind` is `scrub` (segment draw-range) or `layers` (layer-range build-up); `holdFrames` repeats the
+final frame so the loop pauses on the finished model. Encoding uses the Playwright-bundled ffmpeg
+(auto-located; override with `FFMPEG_PATH`), which is a stripped `--disable-everything` build: it can
+only **decode mjpeg/vp8** and **mux webm**, so frames are captured as **JPEG** and piped through
+`image2pipe` → VP8 (no PNG decode, palette filters, or gif muxer exist — see `lib/browser.mjs`
+`encodeWebm`). Reach for animation only when a static frame genuinely can't carry the feature.
diff --git a/tools/screenshots/capture.mjs b/tools/screenshots/capture.mjs
index dd43998..39424a9 100644
--- a/tools/screenshots/capture.mjs
+++ b/tools/screenshots/capture.mjs
@@ -21,7 +21,7 @@
 import { fileURLToPath } from 'node:url';
 import { dirname, resolve } from 'node:path';
 import { readFileSync } from 'node:fs';
-import { launchBrowser, readCanvasPng, savePngDataUrl } from './lib/browser.mjs';
+import { launchBrowser, readCanvasPng, savePngDataUrl, encodeWebm } from './lib/browser.mjs';
 import { docTheme, VIEW, SCALE, PAL, DOC_BACKGROUND_CSS } from './lib/presentation.mjs';
 
 const __dirname = dirname(fileURLToPath(import.meta.url));
@@ -188,6 +188,38 @@ async function driveToolpath(page, shot) {
   );
   await page.waitForTimeout(400);
 
+  // Animation: sweep a temporal control across frames and encode a looping WebM.
+  // The camera + theme set above stay fixed; only the draw-range changes. Frames
+  // are JPEG (the bundled ffmpeg can only decode mjpeg, not png — see encodeWebm).
+  if (shot.output === 'webm' && shot.anim) {
+    const spec = shot.anim;
+    const N = spec.frames || 40;
+    const hold = spec.holdFrames || 0; // repeat the final frame so the loop pauses full
+    const frames = [];
+    for (let i = 0; i <= N; i++) {
+      const t = i / N;
+      await page.evaluate(
+        ({ kind, t }) => {
+          const r = window.viewer.renderer;
+          if (kind === 'scrub') {
+            const total = r.segmentCount;
+            r.setScrubPosition(t >= 1 ? null : Math.max(1, Math.round(t * total)));
+          } else if (kind === 'layers') {
+            const last = Math.max(0, r.layerCount - 1);
+            r.setLayerRange(0, Math.max(0, Math.round(t * last)));
+          }
+          r.render();
+        },
+        { kind: spec.kind, t }
+      );
+      await page.waitForTimeout(spec.settleMs || 30);
+      frames.push(await readCanvasPng(page, 'view', true, 'image/jpeg', spec.quality || 0.9));
+    }
+    for (let h = 0; h < hold; h++) frames.push(frames[frames.length - 1]);
+    encodeWebm(frames, resolve(MEDIA, shot.name + '.webm'), { fps: spec.fps || 16, width: spec.width || 720 });
+    return;
+  }
+
   const out = resolve(MEDIA, shot.name + '.png');
   if (shot.fullPage) {
     // page.screenshot stalls on a live WebGL surface under headless SwiftShader.
diff --git a/tools/screenshots/lib/browser.mjs b/tools/screenshots/lib/browser.mjs
index 4e24e7a..256d78e 100644
--- a/tools/screenshots/lib/browser.mjs
+++ b/tools/screenshots/lib/browser.mjs
@@ -15,6 +15,7 @@ import { chromium } from 'playwright-core';
 import { existsSync, readdirSync, writeFileSync } from 'node:fs';
 import { homedir } from 'node:os';
 import { join } from 'node:path';
+import { execFileSync } from 'node:child_process';
 
 function playwrightCacheDir() {
   if (process.platform === 'win32')
@@ -94,19 +95,19 @@ export async function launchBrowser() {
   throw new Error('Could not launch any Chromium candidate:\n' + errors.join('\n'));
 }
 
-/** Copy a WebGL canvas' backing store into a 2D canvas and return a PNG data URL. */
-export async function readCanvasPng(page, canvasId, renderFirst = true) {
+/** Copy a WebGL canvas' backing store into a 2D canvas and return an image data URL. */
+export async function readCanvasPng(page, canvasId, renderFirst = true, mime = 'image/png', quality = 0.92) {
   return page.evaluate(
-    ({ id, renderFirst }) => {
+    ({ id, renderFirst, mime, quality }) => {
       if (renderFirst && window.viewer?.renderer?.render) window.viewer.renderer.render();
       const src = document.getElementById(id);
       const c = document.createElement('canvas');
       c.width = src.width;
       c.height = src.height;
       c.getContext('2d').drawImage(src, 0, 0);
-      return c.toDataURL('image/png');
+      return c.toDataURL(mime, quality);
     },
-    { id: canvasId, renderFirst }
+    { id: canvasId, renderFirst, mime, quality }
   );
 }
 
@@ -114,3 +115,45 @@ export async function readCanvasPng(page, canvasId, renderFirst = true) {
 export function savePngDataUrl(outPath, dataUrl) {
   writeFileSync(outPath, Buffer.from(dataUrl.split(',')[1], 'base64'));
 }
+
+const dataUrlToBuffer = (u) => Buffer.from(u.split(',')[1], 'base64');
+
+/**
+ * Encode an array of JPEG frames (each a `data:image/jpeg` URL) into a looping,
+ * muted WebM (VP8) via the Playwright-bundled ffmpeg. That build is stripped
+ * (`--disable-everything`): it can only DECODE mjpeg/vp8 and MUX webm, so frames
+ * are piped as concatenated JPEGs through `image2pipe` + the mjpeg decoder — no
+ * PNG decode, palette filters, or gif muxer are available. Throws if ffmpeg is
+ * missing. WebM is embedded via `<video autoplay loop muted playsinline>`.
+ */
+export function encodeWebm(frameDataUrls, outPath, { fps = 16, width = 720 } = {}) {
+  const ffmpeg = resolveFfmpeg();
+  if (!ffmpeg) throw new Error('ffmpeg not found (set FFMPEG_PATH or install a Playwright browser bundle).');
+  const input = Buffer.concat(frameDataUrls.map(dataUrlToBuffer));
+  // -crf/-b:v 0 = constant-quality VP8; scale to an even width for the codec.
+  execFileSync(
+    ffmpeg,
+    [
+      '-y',
+      '-f',
+      'image2pipe',
+      '-c:v',
+      'mjpeg',
+      '-framerate',
+      String(fps),
+      '-i',
+      'pipe:0',
+      '-vf',
+      `scale=${width}:-2:flags=lanczos`,
+      '-c:v',
+      'libvpx',
+      '-b:v',
+      '0',
+      '-crf',
+      '22',
+      '-an',
+      outPath
+    ],
+    { input, stdio: ['pipe', 'ignore', 'inherit'], maxBuffer: 1 << 30 }
+  );
+}
diff --git a/tools/screenshots/shots.manifest.json b/tools/screenshots/shots.manifest.json
index 69f5589..b33c28c 100644
--- a/tools/screenshots/shots.manifest.json
+++ b/tools/screenshots/shots.manifest.json
@@ -202,6 +202,30 @@
       "color": { "mode": "feature", "fallback": [0.55, 0.55, 0.55] },
       "caption": "Line geometry: flat one-pixel paths — lighter, for very large files or low-GPU devices.",
       "alt": "The calicat rendered as flat single-pixel toolpath lines"
+    },
+    {
+      "name": "scrub-sweep",
+      "page": "toolpath",
+      "class": "feature-proof",
+      "file": "gcodes/3DBenchy.gcode",
+      "quality": "tubes",
+      "color": { "mode": "feature", "fallback": [0.55, 0.55, 0.55] },
+      "output": "webm",
+      "anim": { "kind": "scrub", "frames": 48, "fps": 16, "holdFrames": 10 },
+      "caption": "Segment scrub: stepping the draw-range through the toolpath traces the exact print order — the animation IS the feature.",
+      "alt": "Animation of 3DBenchy drawing itself as the segment scrub sweeps from the first move to the last"
+    },
+    {
+      "name": "layer-buildup",
+      "page": "toolpath",
+      "class": "feature-proof",
+      "file": "gcodes/3DBenchy.gcode",
+      "quality": "tubes",
+      "color": { "mode": "feature", "fallback": [0.55, 0.55, 0.55] },
+      "output": "webm",
+      "anim": { "kind": "layers", "frames": 44, "fps": 16, "holdFrames": 10 },
+      "caption": "Layer-range sweep: raising the top layer builds the model up bottom to top — the progressive reveal, shown as motion.",
+      "alt": "Animation of 3DBenchy building up layer by layer from the base to the top as the layer range grows"
     }
   ]
 }