diff --git a/docs/systems/uploads.md b/docs/systems/uploads.md
index 7b45da7d..3cd547a3 100644
--- a/docs/systems/uploads.md
+++ b/docs/systems/uploads.md
@@ -164,6 +164,7 @@ Processing occurs inline during upload, before the response is sent. All process
      - `1` / `true` — web-standard codec (H.264/AVC, VP8/VP9, AV1, Theora) in a web container (`video/mp4`, `video/webm`, `video/ogg`). Plays inline.
      - `NULL` — unknown / optimistic. Codec couldn't be probed (ffmpeg absent or probe failed), or it's a web-safe codec in a container with inconsistent cross-browser support (H.264 in .mov). The client attempts inline playback and degrades via the `<video>` `onError` handler.
    - `false` is never widened beyond codecs known to fail everywhere, so an instance without ffmpeg keeps prior behaviour (attempt playback) rather than regressing every video to "unplayable".
+   - **The verdict is computed Chromium-first and is not authoritative per-client.** Web-playability of HEVC is browser-dependent — WebKit (Safari/iOS) decodes it via the OS while Chromium/Firefox/Electron don't. The client therefore treats `playable === false` as "needs a capability check": it pre-renders the fallback only when the current browser also can't decode the format (`BROWSER_SUPPORTS_HEVC` in `AttachmentRenderer.tsx`). See §9 Attachment Rendering.
 
 ### Audio Processing
 
@@ -532,7 +533,7 @@ URL resolution for attachment/thumbnail:
 | MIME category | Rendering |
 |---------------|-----------|
 | `image/*` | `<img>` with click-to-preview, lazy loading, aspect ratio from width/height, max 400x300px, uses thumbnail if available |
-| `video/*` | `VideoAttachment` sub-component. Playable (`playable !== false`): `<video src>` with native controls, poster from thumbnail, preload `none` (with dimensions) or `metadata` (without), max 400px wide / 300px tall, with an `onError` handler that falls back to the download card. Unplayable (`playable === false`, e.g. HEVC .mov): renders the download card directly — poster (if any) under a "Can't play here — download" overlay, plus filename, duration, size and a one-tap download. Never a silently broken player. |
+| `video/*` | `VideoAttachment` sub-component. Playable (`playable !== false`): `<video src>` with native controls, poster from thumbnail, preload `none` (with dimensions) or `metadata` (without), max 400px wide / 300px tall, with an `onError` handler that falls back to the download card. Unplayable (`playable === false`, e.g. HEVC .mov): renders the download card directly — poster (if any) under a "Can't play here — download" overlay, plus filename, duration, size and a one-tap download. **Browser-aware:** the `playable === false` verdict is computed Chromium-first, so the client only pre-fails when *this* browser also can't decode the format. WebKit (Safari/iOS) decodes HEVC via the OS, so a Safari user still gets inline playback (gated on `BROWSER_SUPPORTS_HEVC`, a one-time `canPlayType` probe for `hvc1`/`hev1`); the `onError` handler remains the safety net. Never a silently broken player. |
 | `audio/*` | Audio card with icon, filename, size, `<audio>` with native controls, preload `metadata`, max 420px wide |
 | Other | Download link card with file icon, filename (link-styled), size |
 
diff --git a/packages/web/src/components/chat/AttachmentRenderer.tsx b/packages/web/src/components/chat/AttachmentRenderer.tsx
index 86464dd2..17350eec 100644
--- a/packages/web/src/components/chat/AttachmentRenderer.tsx
+++ b/packages/web/src/components/chat/AttachmentRenderer.tsx
@@ -24,6 +24,26 @@ function formatDuration(seconds: number): string {
   return `${m}:${s.toString().padStart(2, '0')}`;
 }
 
+/**
+ * Whether *this* browser can decode HEVC (H.265) in a <video> element.
+ *
+ * Web-playability of HEVC is browser-dependent, so the server's `playable`
+ * flag (computed Chromium-first) can't be authoritative for every client:
+ * WebKit (Safari on macOS/iOS) decodes HEVC via the OS, while Chromium,
+ * Firefox and stock Electron cannot. HEVC is the codec that the server's
+ * "unplayable" verdict effectively hinges on, so we probe for it here and let
+ * capable browsers attempt playback rather than blindly showing the fallback.
+ *
+ * Computed once at module load. `canPlayType` returns '' when unsupported and
+ * 'maybe'/'probably' otherwise; Safari reports support for the hvc1/hev1 tags.
+ */
+const BROWSER_SUPPORTS_HEVC: boolean = (() => {
+  if (typeof document === 'undefined') return false;
+  const v = document.createElement('video');
+  return v.canPlayType('video/mp4; codecs="hvc1"') !== '' ||
+    v.canPlayType('video/mp4; codecs="hev1"') !== '';
+})();
+
 /**
  * Resolves the displayable URL for an attachment. Same logic used by inline
  * `<img>`/`<video>`/`<audio>` rendering and the file-card download button —
@@ -49,16 +69,23 @@ interface VideoAttachmentProps {
  *
  *   1. Proactive — the server classifies web-playability from the probed codec
  *      (`attachment.playable === false`), so we render the download card
- *      directly with no flash of a dead player.
- *   2. Reactive — for the optimistic/unknown cases, the `<video>` `onError`
- *      handler flips to the same card if playback actually fails at runtime.
+ *      directly with no flash of a dead player. This is honoured only when the
+ *      current browser also can't decode the format: the server flag is
+ *      Chromium-first, but WebKit (Safari/iOS) decodes HEVC, so a Safari user
+ *      still gets inline playback (see `BROWSER_SUPPORTS_HEVC`).
+ *   2. Reactive — for the optimistic/unknown cases, and for capable browsers
+ *      attempting a flagged file, the `<video>` `onError` handler flips to the
+ *      same card if playback actually fails at runtime.
  *
  * The fallback card surfaces the poster (still a useful preview), filename,
  * duration and size, and a one-tap download — never a silently broken player.
  */
 function VideoAttachment({ attachment, attUrl, thumbUrl, federationInlineBadge }: VideoAttachmentProps) {
   const startDownload = useTransferStore((s) => s.startDownload);
-  const [failed, setFailed] = useState(attachment.playable === false);
+  // Pre-fail only when the server flagged it unplayable AND this browser can't
+  // decode it anyway. Capable browsers (Safari/WebKit ⇒ HEVC) attempt playback
+  // and fall back via onError if it genuinely fails.
+  const [failed, setFailed] = useState(attachment.playable === false && !BROWSER_SUPPORTS_HEVC);
 
   const { width, height, originalName, mimetype, size, duration } = attachment;
   const hasDimensions = !!(width && height);