diff --git a/media/teaser/README.md b/media/teaser/README.md
index db4b114..442bbe3 100644
--- a/media/teaser/README.md
+++ b/media/teaser/README.md
@@ -69,6 +69,7 @@ game's store captures and renders:
 cd examples/demo-game && bun serve.ts & bun ../../cli/index.ts shots capture && bun ../../cli/index.ts shots fonts && bun ../../cli/index.ts shots render
 # from the repo root
 bun media/teaser/render.ts > media/teaser/out/render.log 2>&1 &   # master, sound, poster, web version: about 20 min
+bun media/teaser/render.ts --scale 2 > media/teaser/out/render-4k.log 2>&1 &   # 3840x2160 master for X (about 40 Mbps, AAC 320k): about 45 min
 bun media/teaser/render.ts --desktop                                # capture the desktop app frames again (after a UI change)
 bun media/teaser/render.ts --animatic ../storebound-dist/teaser-v9-animatic  # draft.mp4 (960x540), contact-sheet.png, shots.md: for the owner's OK
 bun media/teaser/render.ts --stills 2.5,13.5,38                     # PNG stills in out/stills for a quick layout check
diff --git a/media/teaser/desktop.ts b/media/teaser/desktop.ts
index 083e397..67a351b 100644
--- a/media/teaser/desktop.ts
+++ b/media/teaser/desktop.ts
@@ -39,7 +39,7 @@ import { launch } from '../../cli/shots/browser';
 
 const DIR = import.meta.dir;
 const ROOT = join(DIR, '../..');
-const OUT = join(DIR, 'out/desktop');
+const DEFAULT_OUT = join(DIR, 'out/desktop');
 export const VIEW = { width: 1280, height: 800 };
 const log = (m: string): void => console.log(`${new Date().toISOString().slice(11, 19)} [desktop] ${m}`);
 
@@ -64,7 +64,9 @@ export function realConsolePlan(form: string): Record<string, unknown> {
   } finally { rmSync(dir, { recursive: true, force: true }); }
 }
 
-export async function captureDesktop(): Promise<void> {
+/** `scale` is the device scale of the captures (2: 2560x1600, the default; 3 for the 4K master), `dir` where they go. */
+export async function captureDesktop(o: { scale?: number; dir?: string } = {}): Promise<void> {
+  const OUT = o.dir ?? DEFAULT_OUT, SCALE = o.scale ?? 2;
   mkdirSync(OUT, { recursive: true });
   const privacyPlan = realConsolePlan('apple-app-privacy');
   const port = 14_300 + Math.floor(Math.random() * 500);
@@ -84,7 +86,7 @@ export async function captureDesktop(): Promise<void> {
     const errors: string[] = [];
 
     const session = async (clean: boolean, waiting = false) => {
-      const ctx = await browser.newContext({ viewport: VIEW, deviceScaleFactor: 2, colorScheme: 'dark', reducedMotion: 'reduce' });
+      const ctx = await browser.newContext({ viewport: VIEW, deviceScaleFactor: SCALE, colorScheme: 'dark', reducedMotion: 'reduce' });
       // the console plan panel shows the real plan of the CLI instead of the fixture's shortened one; after the submit
       // (waiting), the fixture's apple status holds the new submission waiting for review
       await ctx.route(/\/src\/dev\/submit-fixtures\.ts/, async (route: any) => {
diff --git a/media/teaser/render.ts b/media/teaser/render.ts
index a6cd068..a76f3c3 100644
--- a/media/teaser/render.ts
+++ b/media/teaser/render.ts
@@ -9,6 +9,10 @@
 //   bun media/teaser/render.ts --animatic <dir>  the animatic for the owner's OK before any final render: draft.mp4
 //                                                 (960x540, 30 fps, quick encode, with sound), contact-sheet.png
 //                                                 (one frame per second, timestamped), shots.md, checks.json
+//   bun media/teaser/render.ts --scale 2          the 3840x2160 master for 4K uploads: the same page at device scale 2
+//                                                 (text and terminals rendered natively), the desktop frames captured
+//                                                 at @3x (out/desktop@3x), the demo game renders at 2x (out/assets@2x),
+//                                                 H.264 high at about 40 Mbps, AAC 320 kbps; no web version
 //   bun media/teaser/render.ts --serve            preview server: open /index.html?play=1 (or ?t=12.5)
 // Needs ffmpeg and Playwright (devDependency; Playwright's Chromium or an installed Google Chrome), and the demo game's
 // store renders (examples/demo-game: `shots capture`, `shots fonts`, `shots render`, see its README).
@@ -20,11 +24,18 @@ import { captureDesktop } from './desktop';
 const DIR = import.meta.dir;
 const ROOT = join(DIR, '../..');
 const OUT = join(DIR, 'out');
-const ASSETS = join(OUT, 'assets');
 const args = process.argv.slice(2);
 const opt = (k: string): string | undefined => { const i = args.indexOf(`--${k}`); return i >= 0 ? args[i + 1] : undefined; };
 /** 16:9 only. */
 const FORMAT = { w: 1920, h: 1080 };
+/** --scale 2: the page keeps its 1920x1080 layout and renders at this device scale (3840x2160). */
+const SCALE = Number(opt('scale') ?? 1);
+if (SCALE !== 1 && SCALE !== 2) throw new Error('--scale takes 1 or 2');
+const OUT_W = FORMAT.w * SCALE, OUT_H = FORMAT.h * SCALE;
+/** The desktop frames' device scale: the deepest push shows a 1280 px frame at about 1.43 CSS px per px, so 4K needs @3x. */
+const DESK_DIR = SCALE > 1 ? 'desktop@3x' : 'desktop';
+const ASSET_DIR = SCALE > 1 ? `assets@${SCALE}x` : 'assets';
+const ASSETS = join(OUT, ASSET_DIR);
 /** The web version: 1280x720 H.264, two-pass to about this many bytes (about 830 kbps video for 58 s). */
 const WEB_BYTES = 6.7e6;
 const CAPTURE_FPS = 60;
@@ -49,7 +60,7 @@ function prepAssets(): void {
   for (const lang of ['en', 'tr', 'ja', 'ar']) for (const size of ['ios69', 'ios65', 'ipad13', 'play', 'tab7', 'tab10', 'feature']) {
     const src = join(renders, lang, size, size === 'feature' ? '1024x500.png' : '01.png');
     if (!existsSync(src)) { missing.push(`${lang}/${size}`); continue; }
-    ff('-i', src, '-vf', size === 'feature' ? 'scale=600:-2:flags=lanczos' : 'scale=-2:360:flags=lanczos', '-q:v', '3', join(dir, `${lang}-${size}.jpg`));
+    ff('-i', src, '-vf', size === 'feature' ? `scale=${Math.min(1024, 600 * SCALE)}:-2:flags=lanczos` : `scale=-2:${360 * SCALE}:flags=lanczos`, '-q:v', '3', join(dir, `${lang}-${size}.jpg`));
     n++;
   }
   // the game's own screens (its store captures, before any framing): the opening scene
@@ -59,7 +70,7 @@ function prepAssets(): void {
   for (const id of ['play', 'combo', 'map', 'stars']) {
     const src = join(ROOT, 'examples/demo-game/store/shots/frames/en/phone', `${id}.png`);
     if (!existsSync(src)) { missing.push(`frames/en/phone/${id}`); continue; }
-    ff('-i', src, '-vf', 'scale=-2:1100:flags=lanczos', '-q:v', '2', join(game, `${id}.jpg`));
+    ff('-i', src, '-vf', `scale=-2:${1100 * SCALE}:flags=lanczos`, '-q:v', '2', join(game, `${id}.jpg`));
     n++;
   }
   if (missing.length) throw new Error(`demo game renders missing (${missing.slice(0, 4).join(', ')}${missing.length > 4 ? ', ...' : ''}): run its shots capture, fonts and render first (examples/demo-game/README.md)`);
@@ -70,7 +81,10 @@ function serve(): ReturnType<typeof Bun.serve> {
   return Bun.serve({
     port: Number(opt('port') ?? 0),
     fetch(req) {
-      const p = decodeURIComponent(new URL(req.url).pathname).replace(/^\/+/, '') || 'index.html';
+      let p = decodeURIComponent(new URL(req.url).pathname).replace(/^\/+/, '') || 'index.html';
+      // --scale 2: the page asks for out/desktop and out/assets; serve the higher-resolution captures in their place
+      if (p.startsWith('out/desktop/')) p = `out/${DESK_DIR}/${p.slice('out/desktop/'.length)}`;
+      else if (p.startsWith('out/assets/')) p = `out/${ASSET_DIR}/${p.slice('out/assets/'.length)}`;
       if (p.includes('..')) return new Response('no', { status: 400 });
       // the logo comes from the repo's brand/ folder (tools/brand-assets.py) and the app icon from the demo game, not copies
       const f = Bun.file(p.startsWith('brand/') || p.startsWith('examples/demo-game/store/icon/') ? join(ROOT, p) : join(DIR, p));
@@ -82,7 +96,7 @@ function serve(): ReturnType<typeof Bun.serve> {
 async function main(): Promise<void> {
   mkdirSync(OUT, { recursive: true });
   prepAssets();
-  if (args.includes('--desktop') || !existsSync(join(OUT, 'desktop/boxes.json'))) await captureDesktop();
+  if (args.includes('--desktop') || !existsSync(join(OUT, DESK_DIR, 'boxes.json'))) await captureDesktop(SCALE > 1 ? { scale: 3, dir: join(OUT, DESK_DIR) } : {});
   const server = serve();
   const base = `http://127.0.0.1:${server.port}/index.html`;
   if (args.includes('--serve')) { log(`preview: ${base}?play=1`); return; }
@@ -95,7 +109,7 @@ async function main(): Promise<void> {
     const soundOnly = args.includes('--sound');
     if (!soundOnly) {
       const f = FORMAT;
-      const page = await browser.newPage({ viewport: { width: f.w, height: f.h }, deviceScaleFactor: 1 });
+      const page = await browser.newPage({ viewport: { width: f.w, height: f.h }, deviceScaleFactor: SCALE });
       const errors: string[] = [];
       page.on('pageerror', (e: Error) => errors.push(e.message));
       page.on('response', (r: any) => { if (r.status() >= 400 && !r.url().endsWith('/favicon.ico')) errors.push(`${r.status()} ${r.url()}`); });
@@ -117,10 +131,12 @@ async function main(): Promise<void> {
       }
       // 60 fps capture, then each pair of frames is averaged into one 30 fps frame (motion blur on fast moves)
       const frames = Math.round(DURATION * CAPTURE_FPS);
-      const silent = join(OUT, `teaser-${f.w}x${f.h}-silent.mp4`);
+      const silent = join(OUT, `teaser-${OUT_W}x${OUT_H}-silent.mp4`);
+      // 1080p: CRF 16; 4K for X: about 40 Mbps (41 s, about 210 MB, under X's 512 MB)
+      const rate = SCALE > 1 ? ['-b:v', '40M', '-maxrate', '50M', '-bufsize', '80M'] : ['-crf', '16'];
       const enc = Bun.spawn(['ffmpeg', '-hide_banner', '-loglevel', 'error', '-y', '-f', 'image2pipe', '-framerate', String(CAPTURE_FPS), '-c:v', 'png', '-i', '-',
         '-vf', `tmix=frames=2:weights='1 1',select='not(mod(n\\,2))',setpts=N/${FPS}/TB`, '-r', String(FPS),
-        '-c:v', 'libx264', '-profile:v', 'high', '-preset', 'slow', '-crf', '16', '-pix_fmt', 'yuv420p',
+        '-c:v', 'libx264', '-profile:v', 'high', '-preset', 'slow', ...rate, '-pix_fmt', 'yuv420p',
         '-g', String(FPS * 2), '-movflags', '+faststart', silent], { stdin: 'pipe', stdout: 'inherit', stderr: 'inherit' });
       const t0 = Date.now();
       for (let i = 0; i < frames; i++) {
@@ -134,7 +150,7 @@ async function main(): Promise<void> {
       await enc.stdin.end();
       if (await enc.exited !== 0) throw new Error('ffmpeg encode failed');
       if (errors.length) throw new Error(`page errors:\n  ${[...new Set(errors)].join('\n  ')}`);
-      ff('-ss', String(DURATION - 0.5), '-i', silent, '-frames:v', '1', '-q:v', '3', join(OUT, `poster-${f.w}x${f.h}.jpg`));
+      ff('-ss', String(DURATION - 0.5), '-i', silent, '-frames:v', '1', '-q:v', '3', join(OUT, `poster-${OUT_W}x${OUT_H}.jpg`));
       log(`${silent} (${(statSync(silent).size / 1e6).toFixed(1)} MB)`);
       await page.close();
     }
@@ -158,12 +174,12 @@ async function main(): Promise<void> {
     ff('-i', raw, '-af', `volume=${gain.toFixed(2)}dB,afade=t=out:st=${(dur - 1).toFixed(2)}:d=1,aresample=48000`,
       '-c:a', 'pcm_s16le', '-ar', '48000', '-ac', '2', music);
     if (!soundOnly) {
-      const silent = join(OUT, `teaser-${FORMAT.w}x${FORMAT.h}-silent.mp4`), out = join(OUT, `teaser-${FORMAT.w}x${FORMAT.h}.mp4`);
+      const silent = join(OUT, `teaser-${OUT_W}x${OUT_H}-silent.mp4`), out = join(OUT, `teaser-${OUT_W}x${OUT_H}.mp4`);
       if (!existsSync(silent)) throw new Error(`${silent} missing`);
-      ff('-i', silent, '-i', music, '-map', '0:v', '-map', '1:a', '-c:v', 'copy', '-c:a', 'aac', '-b:a', '192k', '-ar', '48000', '-ac', '2', '-shortest', '-movflags', '+faststart', out);
+      ff('-i', silent, '-i', music, '-map', '0:v', '-map', '1:a', '-c:v', 'copy', '-c:a', 'aac', '-b:a', SCALE > 1 ? '320k' : '192k', '-ar', '48000', '-ac', '2', '-shortest', '-movflags', '+faststart', out);
       log(`${out} (${(statSync(out).size / 1e6).toFixed(1)} MB)`);
     }
-    if (soundOnly) return;
+    if (soundOnly || SCALE > 1) return;
 
     // web version: 1280x720 H.264, about 6 MB (two-pass), plus its poster
     const h = join(OUT, 'teaser-1920x1080.mp4');