diff --git a/apps/desktop/src/components/assistant-ui/markdown-text.tsx b/apps/desktop/src/components/assistant-ui/markdown-text.tsx
index 15842f15695e..fdcf94e16bb0 100644
--- a/apps/desktop/src/components/assistant-ui/markdown-text.tsx
+++ b/apps/desktop/src/components/assistant-ui/markdown-text.tsx
@@ -27,8 +27,8 @@ import {
   mediaKind,
   mediaName,
   mediaPathFromMarkdownHref,
-  mediaStreamUrl,
-  resolveMediaDisplaySrc
+  resolveMediaDisplaySrc,
+  resolveMediaPlaybackSrc
 } from '@/lib/media'
 import { previewTargetFromMarkdownHref } from '@/lib/preview-targets'
 import { sessionRefFromMarkdownHref } from '@/lib/session-refs'
@@ -98,16 +98,6 @@ function preprocessWithTailRepair(text: string): string {
   }
 }
 
-async function mediaSrc(path: string): Promise<string> {
-  // Stream audio/video through the custom protocol: data URLs are capped and
-  // load the whole file into memory, which broke playback for larger videos.
-  if (window.hermesDesktop && ['audio', 'video'].includes(mediaKind(path))) {
-    return mediaStreamUrl(path)
-  }
-
-  return resolveMediaDisplaySrc(path)
-}
-
 function useOpenMediaFile(path: string) {
   const [openFailed, setOpenFailed] = useState(false)
 
@@ -170,7 +160,7 @@ function MediaAttachment({ path }: { path: string }) {
       }
     }
 
-    void mediaSrc(path)
+    void resolveMediaPlaybackSrc(path)
       .then(value => {
         if (value.startsWith('blob:')) {
           objectUrl = value
diff --git a/apps/desktop/src/lib/media.remote.test.ts b/apps/desktop/src/lib/media.remote.test.ts
index 79676c691431..c16835cd676a 100644
--- a/apps/desktop/src/lib/media.remote.test.ts
+++ b/apps/desktop/src/lib/media.remote.test.ts
@@ -11,7 +11,8 @@ import {
   isInlineMediaSrc,
   isRemoteGateway,
   mediaExternalUrl,
-  resolveMediaDisplaySrc
+  resolveMediaDisplaySrc,
+  resolveMediaPlaybackSrc
 } from './media'
 
 describe('isRemoteGateway', () => {
@@ -139,6 +140,40 @@ describe('resolveMediaDisplaySrc', () => {
   })
 })
 
+describe('resolveMediaPlaybackSrc', () => {
+  afterEach(() => {
+    vi.unstubAllGlobals()
+    $connection.set(null)
+  })
+
+  it('keeps a remote HTTPS video URL unchanged', async () => {
+    vi.stubGlobal('window', { hermesDesktop: { api: vi.fn() } })
+    $connection.set({ mode: 'remote', baseUrl: 'https://gateway.test', token: 'secret' } as never)
+
+    await expect(resolveMediaPlaybackSrc('https://cdn.example.com/render.mp4')).resolves.toBe(
+      'https://cdn.example.com/render.mp4'
+    )
+  })
+
+  it('routes gateway-local video through the authenticated download endpoint', async () => {
+    vi.stubGlobal('window', { hermesDesktop: { api: vi.fn() } })
+    $connection.set({ mode: 'remote', baseUrl: 'https://gateway.test', token: 's e/cret' } as never)
+
+    await expect(resolveMediaPlaybackSrc('/root/outputs/render.mp4')).resolves.toBe(
+      'https://gateway.test/api/files/download?path=%2Froot%2Foutputs%2Frender.mp4&token=s%20e%2Fcret'
+    )
+  })
+
+  it('uses the Electron streaming protocol for local desktop video', async () => {
+    vi.stubGlobal('window', { hermesDesktop: { api: vi.fn() } })
+    $connection.set({ mode: 'local' } as never)
+
+    await expect(resolveMediaPlaybackSrc('C:\\renders\\demo.mp4')).resolves.toBe(
+      'hermes-media://stream/C%3A%5Crenders%5Cdemo.mp4'
+    )
+  })
+})
+
 describe('gatewayMediaDataUrl', () => {
   const api = vi.fn(async ({ path }: { path: string }) => {
     if (path.startsWith('/api/fs/read-data-url?')) {
diff --git a/apps/desktop/src/lib/media.ts b/apps/desktop/src/lib/media.ts
index c392caa4d7bd..33bcfbd963f8 100644
--- a/apps/desktop/src/lib/media.ts
+++ b/apps/desktop/src/lib/media.ts
@@ -82,6 +82,22 @@ export async function resolveMediaDisplaySrc(path: string): Promise<string> {
   return window.hermesDesktop.readFileDataUrl(filePathFromMediaPath(path))
 }
 
+// Audio/video need a seekable source instead of a whole-file data URL. Keep
+// remote URLs untouched, route gateway-local files through the authenticated
+// download endpoint, and reserve the Electron protocol for files on this
+// desktop machine.
+export async function resolveMediaPlaybackSrc(path: string): Promise<string> {
+  if (isInlineMediaSrc(path)) {
+    return path
+  }
+
+  if (window.hermesDesktop && ['audio', 'video'].includes(mediaKind(path))) {
+    return isRemoteGateway() ? mediaExternalUrl(path) : mediaStreamUrl(path)
+  }
+
+  return resolveMediaDisplaySrc(path)
+}
+
 // Resolve a media path to a URL the shell can open. Remote mode rewrites
 // gateway-local paths to an authenticated /api/files/download URL (the file
 // lives on the gateway, not this disk); local mode keeps the file:// form.