diff --git a/.env.docker.example b/.env.docker.example
index 8a4331b..0474610 100644
--- a/.env.docker.example
+++ b/.env.docker.example
@@ -34,7 +34,8 @@ TRUSTED_PROXY_MODE="nginx"
 MINIO_ROOT_USER="replace-with-minio-root-user"
 MINIO_ROOT_PASSWORD="replace-with-strong-minio-password"
 R2_ENDPOINT="http://minio:9000"
-# Browser-facing endpoint used for presigned upload URLs (must be reachable from the browser).
+# Browser-facing MinIO origin for presigned upload URLs (scheme + host, no path).
+# Use your public MinIO domain when behind a reverse proxy, e.g. https://minio.example.com
 R2_PRESIGN_ENDPOINT="http://localhost:9000"
 R2_PUBLIC_BASE_URL="http://localhost:9000/openframe"
 R2_ACCESS_KEY_ID="replace-with-minio-root-user"
diff --git a/Dockerfile b/Dockerfile
index 846fbe8..391f3dd 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -16,6 +16,7 @@ COPY scripts ./scripts
 COPY types ./types
 COPY components.json ./components.json
 COPY next.config.ts ./next.config.ts
+COPY proxy.ts ./proxy.ts
 COPY postcss.config.mjs ./postcss.config.mjs
 COPY prisma.config.ts ./prisma.config.ts
 COPY tsconfig.json ./tsconfig.json
@@ -36,6 +37,7 @@ RUN apt-get update \
 COPY --from=build /app/package.json ./package.json
 COPY --from=build /app/bun.lock ./bun.lock
 COPY --from=build /app/next.config.ts ./next.config.ts
+COPY --from=build /app/proxy.ts ./proxy.ts
 COPY --from=build /app/public ./public
 COPY --from=build /app/prisma ./prisma
 COPY --from=build /app/scripts ./scripts
diff --git a/README.md b/README.md
index 7965869..9206f12 100644
--- a/README.md
+++ b/README.md
@@ -178,9 +178,16 @@ Behavior when disabled:
 
 - `OPENFRAME_ENABLE_STRIPE=false` disables Stripe checkout and customer portal flows and removes billing-based workspace restrictions.
 - `OPENFRAME_ENABLE_BUNNY_UPLOADS=false` hides Bunny direct-upload entry points. URL-based providers such as YouTube remain available.
-- `OPENFRAME_ENABLE_S3_VIDEO_UPLOADS=true` (with `R2_*` configured) enables presigned uploads to your own S3-compatible storage. Set `OPENFRAME_ENABLE_BUNNY_UPLOADS=false` — only one direct-upload backend can be active. The bucket must allow CORS `PUT` from your app origin (for example `http://localhost:3000` in dev and your production URL). For Docker + MinIO, keep `R2_ENDPOINT=http://minio:9000` (app-internal) and set `R2_PRESIGN_ENDPOINT=http://localhost:9000` (browser-reachable host).
+- `OPENFRAME_ENABLE_S3_VIDEO_UPLOADS=true` (with `R2_*` configured) enables presigned uploads to your own S3-compatible storage. Set `OPENFRAME_ENABLE_BUNNY_UPLOADS=false` — only one direct-upload backend can be active. The bucket must allow CORS `PUT` from your app origin (for example `http://localhost:3000` in dev and your production URL). For Docker + MinIO, keep `R2_ENDPOINT=http://minio:9000` (app-internal) and set `R2_PRESIGN_ENDPOINT` to the browser-reachable MinIO origin (for example `http://localhost:9000` locally, or `https://minio.example.com` when MinIO is behind a reverse proxy). Use the origin only — no path suffix. The app's Content-Security-Policy is generated from runtime env at request time, so published Docker images pick up custom `R2_PRESIGN_ENDPOINT` values without rebuilding or editing `next.config.ts`.
 - `OPENFRAME_REQUIRE_INVITE_CODE=false` allows open registration while keeping invitation-link registration intact.
 
+For self-hosted MinIO behind a reverse proxy, choose one of these browser-facing layouts:
+
+- Separate storage host: route `https://minio.example.com` to MinIO and set `R2_PRESIGN_ENDPOINT=https://minio.example.com` plus `R2_PUBLIC_BASE_URL=https://minio.example.com/openframe`.
+- Same app host: route the bucket path, for example `https://openframe.example.com/openframe/*`, to MinIO and keep all other paths routed to the OpenFrame app. Set `R2_PRESIGN_ENDPOINT=https://openframe.example.com` and `R2_PUBLIC_BASE_URL=https://openframe.example.com/openframe`.
+
+Do not add an extra path prefix such as `/s3` in front of the bucket unless your proxy rewrites it away before MinIO sees the request. S3 path-style presigned URLs expect the first path segment to be the bucket name, so `/openframe/videos/...` is valid while `/s3/openframe/videos/...` makes MinIO treat `s3` as the bucket.
+
 These integrations remain optional for self-hosted deployments and can be enabled later by setting the related environment variables:
 
 - Stripe billing
diff --git a/lib/content-security-policy.ts b/lib/content-security-policy.ts
new file mode 100644
index 0000000..aa26022
--- /dev/null
+++ b/lib/content-security-policy.ts
@@ -0,0 +1,96 @@
+function resolveBunnyCdnHostname(): string | null {
+  const raw = process.env.BUNNY_CDN_URL || process.env.NEXT_PUBLIC_BUNNY_CDN_URL;
+  if (!raw) return null;
+  try {
+    const parsed = new URL(raw);
+    return parsed.hostname || null;
+  } catch {
+    return raw.replace(/^https?:\/\//, '').replace(/\/+$/, '') || null;
+  }
+}
+
+function resolveR2ConnectOrigins(): string[] {
+  const origins = new Set<string>();
+
+  for (const raw of [
+    process.env.R2_ENDPOINT?.trim(),
+    process.env.R2_PRESIGN_ENDPOINT?.trim(),
+    process.env.R2_PUBLIC_BASE_URL?.trim(),
+  ]) {
+    if (!raw) continue;
+    try {
+      origins.add(new URL(raw).origin);
+    } catch {
+      // Ignore invalid custom endpoints in CSP generation.
+    }
+  }
+
+  const accountId = process.env.R2_ACCOUNT_ID?.trim();
+  const bucket = process.env.R2_BUCKET_NAME?.trim();
+  if (accountId) {
+    origins.add(`https://${accountId}.r2.cloudflarestorage.com`);
+    if (bucket) {
+      origins.add(`https://${bucket}.${accountId}.r2.cloudflarestorage.com`);
+    }
+    origins.add('https://*.r2.cloudflarestorage.com');
+  }
+
+  // Docker/MinIO self-hosted defaults for local development.
+  origins.add('http://localhost:9000');
+  origins.add('http://127.0.0.1:9000');
+
+  return [...origins];
+}
+
+/**
+ * Build Content-Security-Policy from runtime environment variables.
+ * Called per request so Docker/self-hosted storage endpoints are available
+ * without rebuilding the image.
+ */
+export function buildContentSecurityPolicy(): string {
+  const isDev = process.env.NODE_ENV === 'development';
+  const bunnyCdnHostname = resolveBunnyCdnHostname();
+  const cdnOrigin = bunnyCdnHostname ? `https://${bunnyCdnHostname}` : '';
+
+  const connectSrcParts = [
+    "'self'",
+    'https://video.bunnycdn.com',
+    'https://www.youtube.com',
+    cdnOrigin,
+    ...resolveR2ConnectOrigins(),
+    // Allow Next.js HMR websocket in development
+    ...(isDev ? ['ws://localhost:* wss://localhost:*'] : []),
+  ].filter(Boolean);
+
+  const imgSrcParts = [
+    "'self'",
+    'data:',
+    'blob:',
+    'https://img.youtube.com',
+    'https://i.ytimg.com',
+    'https://images.unsplash.com',
+    'https://vz-thumbnail.b-cdn.net',
+    cdnOrigin,
+  ].filter(Boolean);
+
+  const mediaSrcParts = ["'self'", 'blob:', cdnOrigin].filter(Boolean);
+
+  return [
+    "default-src 'self'",
+    // 'unsafe-inline' is required by Next.js App Router (hydration scripts, inline styles)
+    // https://www.youtube.com is required for the dynamically-injected YouTube IFrame API script
+    "script-src 'self' 'unsafe-inline' https://www.youtube.com",
+    "style-src 'self' 'unsafe-inline'",
+    `img-src ${imgSrcParts.join(' ')}`,
+    `media-src ${mediaSrcParts.join(' ')}`,
+    "frame-src 'self' https://www.youtube.com https://iframe.mediadelivery.net",
+    `connect-src ${connectSrcParts.join(' ')}`,
+    // next/font self-hosts Google Fonts at build time — no external font origin needed
+    "font-src 'self'",
+    "worker-src 'self' blob:",
+    "object-src 'none'",
+    "base-uri 'self'",
+    "form-action 'self'",
+    "frame-ancestors 'none'",
+  ].join('; ');
+}
diff --git a/next.config.ts b/next.config.ts
index 4f5cf82..74b4694 100644
--- a/next.config.ts
+++ b/next.config.ts
@@ -13,90 +13,10 @@ function resolveBunnyCdnHostname(): string | null {
 }
 
 const bunnyCdnHostname = resolveBunnyCdnHostname();
-const isDev = process.env.NODE_ENV === 'development';
-
-function resolveR2ConnectOrigins(): string[] {
-  const origins = new Set<string>();
-
-  for (const raw of [
-    process.env.R2_ENDPOINT?.trim(),
-    process.env.R2_PRESIGN_ENDPOINT?.trim(),
-    process.env.R2_PUBLIC_BASE_URL?.trim(),
-  ]) {
-    if (!raw) continue;
-    try {
-      origins.add(new URL(raw).origin);
-    } catch {
-      // Ignore invalid custom endpoints in CSP generation.
-    }
-  }
-
-  const accountId = process.env.R2_ACCOUNT_ID?.trim();
-  const bucket = process.env.R2_BUCKET_NAME?.trim();
-  if (accountId) {
-    origins.add(`https://${accountId}.r2.cloudflarestorage.com`);
-    if (bucket) {
-      origins.add(`https://${bucket}.${accountId}.r2.cloudflarestorage.com`);
-    }
-    origins.add('https://*.r2.cloudflarestorage.com');
-  }
-
-  // Docker/MinIO self-hosted defaults. Keep unconditional because CSP is
-  // compiled at build time and build env may not include runtime self-hosted
-  // variables.
-  origins.add('http://localhost:9000');
-  origins.add('http://127.0.0.1:9000');
-
-  return [...origins];
-}
-
-// Build Content-Security-Policy from resolved config
-const cdnOrigin = bunnyCdnHostname ? `https://${bunnyCdnHostname}` : '';
-
-const connectSrcParts = [
-  "'self'",
-  'https://video.bunnycdn.com',
-  'https://www.youtube.com',
-  cdnOrigin,
-  ...resolveR2ConnectOrigins(),
-  // Allow Next.js HMR websocket in development
-  ...(isDev ? ['ws://localhost:* wss://localhost:*'] : []),
-].filter(Boolean);
-
-const imgSrcParts = [
-  "'self'",
-  'data:',
-  'blob:',
-  'https://img.youtube.com',
-  'https://i.ytimg.com',
-  'https://images.unsplash.com',
-  'https://vz-thumbnail.b-cdn.net',
-  cdnOrigin,
-].filter(Boolean);
-
-const mediaSrcParts = ["'self'", 'blob:', cdnOrigin].filter(Boolean);
-
-const contentSecurityPolicy = [
-  "default-src 'self'",
-  // 'unsafe-inline' is required by Next.js App Router (hydration scripts, inline styles)
-  // https://www.youtube.com is required for the dynamically-injected YouTube IFrame API script
-  "script-src 'self' 'unsafe-inline' https://www.youtube.com",
-  "style-src 'self' 'unsafe-inline'",
-  `img-src ${imgSrcParts.join(' ')}`,
-  `media-src ${mediaSrcParts.join(' ')}`,
-  "frame-src 'self' https://www.youtube.com https://iframe.mediadelivery.net",
-  `connect-src ${connectSrcParts.join(' ')}`,
-  // next/font self-hosts Google Fonts at build time — no external font origin needed
-  "font-src 'self'",
-  "worker-src 'self' blob:",
-  "object-src 'none'",
-  "base-uri 'self'",
-  "form-action 'self'",
-  "frame-ancestors 'none'",
-].join('; ');
 
+// Content-Security-Policy is set at request time in proxy.ts so runtime storage
+// endpoints (R2_PRESIGN_ENDPOINT, etc.) are available in Docker deployments.
 const securityHeaders = [
-  { key: 'Content-Security-Policy', value: contentSecurityPolicy },
   // Prevent the app from being embedded in foreign iframes (clickjacking)
   { key: 'X-Frame-Options', value: 'DENY' },
   // Prevent MIME-type sniffing on all responses
diff --git a/proxy.ts b/proxy.ts
new file mode 100644
index 0000000..52d5ac4
--- /dev/null
+++ b/proxy.ts
@@ -0,0 +1,20 @@
+import { NextResponse } from 'next/server';
+import { buildContentSecurityPolicy } from '@/lib/content-security-policy';
+
+export function proxy() {
+  const response = NextResponse.next();
+  response.headers.set('Content-Security-Policy', buildContentSecurityPolicy());
+  return response;
+}
+
+export const config = {
+  matcher: [
+    /*
+     * Match all request paths except:
+     * - _next/static (static files)
+     * - _next/image (image optimization files)
+     * - favicon.ico (favicon file)
+     */
+    '/((?!_next/static|_next/image|favicon.ico).*)',
+  ],
+};