diff --git a/CLAUDE.md b/CLAUDE.md
index b869530..05c7919 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -100,6 +100,11 @@ Things worth knowing before editing:
   `<video>` with no data has a natural size of 300x150, and WebKit sizes it from that —
   so one with no poster of its own gets an empty SVG of the right shape as a stand-in,
   without which a portrait video sits in a squat landscape box until you press play.
+- **A page with a video claims the `playback` audio session** (`public/app.js`). iOS
+  hands inline video the ambient session, which the Ring/Silent switch mutes, so
+  without this the video plays and says nothing until it goes fullscreen — and the
+  report that arrives is "this one platform has no sound". The session only activates
+  once something plays, so declaring it costs nothing on a page nobody presses play on.
 - **Never a bare error page.** A failed resolve renders a card carrying the platform, the
   original URL and the copy button. A broken adapter must still leave the link one tap
   away.
diff --git a/README.md b/README.md
index 9ab0e8a..c41c78e 100644
--- a/README.md
+++ b/README.md
@@ -171,6 +171,10 @@ The one exception is Bluesky video, which is an HLS playlist — proxying it wou
 rewriting the manifest and every segment, so it is linked directly. Safari plays HLS
 natively; other browsers show a note.
 
+A page carrying a video asks iOS for the playback audio session. Without it a video
+playing inline is treated as ambience and the Ring/Silent switch mutes it, so the post
+plays perfectly and says nothing unless you go fullscreen.
+
 Resolved posts are cached in memory for an hour, so a reload or a back button doesn't
 drive the browser again.
 
diff --git a/public/app.js b/public/app.js
index 3caef02..8aebcaf 100644
--- a/public/app.js
+++ b/public/app.js
@@ -155,6 +155,19 @@ function setupMedia(media) {
   }
 }
 
+// On iOS a video playing inline gets the "ambient" audio session, which the
+// Ring/Silent switch mutes -- so the post plays perfectly and says nothing,
+// and the only way to hear it is to go fullscreen. Claiming "playback" says
+// what is true here: the sound is the point, not decoration. The session is
+// not activated until something actually plays, so declaring it up front
+// interrupts nothing; it is declared only on a page that has a video so an
+// ordinary text post never claims it at all.
+function setupAudioSession() {
+  if (!('audioSession' in navigator)) return;
+  if (!document.querySelector('video')) return;
+  navigator.audioSession.type = 'playback';
+}
+
 // Every comment is a <details open>, so folding one already works with this
 // file missing. All this adds is doing the whole page at once, which is why
 // the button ships hidden and is only revealed here.
@@ -189,6 +202,7 @@ setupCopy();
 applyBrowser(storedBrowser());
 setupBrowserPicker();
 for (const media of document.querySelectorAll('.media')) setupMedia(media);
+setupAudioSession();
 setupComments();
 
 // --- Verification puzzles -------------------------------------------------