diff --git a/HANDOFF.md b/HANDOFF.md
index 8081bd7..d38c125 100644
--- a/HANDOFF.md
+++ b/HANDOFF.md
@@ -454,9 +454,21 @@ death summary is the end menu, and the zombie bed ducks out as it comes in. Two
   bed's gain at 0. Without it, a multi-megabyte file ducked mid-fetch comes up at full level several
   seconds later, over the match.
 
-`background-music.wav` is 8.3 MB and now downloads on every page load. Converting it to m4a (as the
-umpire lines already are) would cut that ~10x; `loopBed` hardcodes `.wav`, so that is a two-line
-change if it ever matters.
+**The theme is AAC** (`background-music.m4a`, 768 KB — the WAV was 8.3 MB, and this one downloads on
+every page load before the player has decided to play). `loopBed` takes the FULL filename now,
+because the beds are a mix of `.wav` and `.m4a`; `fadeBed`'s key must match it exactly, extension
+included, or a duck silently no-ops.
+
+**A compressed loop needs an explicit `loopEnd`.** AAC pads the final packet, so Chrome decodes this
+48.000 s master to a 48.0174 s buffer — 17 ms of silence spliced in at every seam, once a loop, on
+the title screen. `menuMusic` passes `48`. Re-encode the file and re-measure:
+`fetch(f).then(r=>r.arrayBuffer()).then(a=>new AudioContext().decodeAudioData(a)).then(b=>b.duration)`.
+`zombie-mode.wav` (5.9 MB) is the other candidate for this treatment, and it loads mid-match rather
+than up front, so it matters less.
+
+Measuring which audio files actually loaded: `performance.getEntriesByType('resource')` is USELESS
+here — the ~200 sprite PNGs blow past the 250-entry resource-timing buffer and every later fetch is
+silently dropped from it. Read the network log instead. That cost a wrong "the bed never loaded".
 
 ## Session log: the serve is the gesture (2026-08-01)
 
diff --git a/assets/audio/background-music.m4a b/assets/audio/background-music.m4a
new file mode 100644
index 0000000..ff647fe
Binary files /dev/null and b/assets/audio/background-music.m4a differ
diff --git a/assets/audio/background-music.wav b/assets/audio/background-music.wav
deleted file mode 100644
index bb283a3..0000000
Binary files a/assets/audio/background-music.wav and /dev/null differ
diff --git a/audio.js b/audio.js
index a625a38..b74e1d4 100644
--- a/audio.js
+++ b/audio.js
@@ -77,7 +77,7 @@ export function aww(vol = 1) { sfx('tennis-aww', vol * 0.5, { reverb: true }); }
 // Looping background beds (scene atmosphere, mode music): each starts once, highpass 'lowcut' + quiet gain.
 const beds = new Map(); // file -> {ac, g, vol} once playing (null while loading); see fadeBed
 const ducked = new Set(); // beds asked to duck while they were STILL LOADING — see fadeBed
-function loopBed(file, lowcut, vol) {
+function loopBed(file, lowcut, vol, loopEnd = 0) {
   // audio() FIRST, before the already-started early return: it is also what RESUMES a context the
   // browser suspended under its autoplay policy. The menu theme is started at boot, before any
   // gesture exists, so it plays into a suspended context and stays silent — and the call that has
@@ -86,11 +86,16 @@ function loopBed(file, lowcut, vol) {
   const ac = audio();
   if (beds.has(file)) return;
   beds.set(file, null);
-  fetch('assets/audio/' + file + '.wav')
+  fetch('assets/audio/' + file) // full filename: the beds are a mix of .wav and .m4a, see below
     .then(r => { if (!r.ok) throw 0; return r.arrayBuffer(); })
     .then(ab => ac.decodeAudioData(ab))
     .then(buf => {
       const src = ac.createBufferSource(); src.buffer = buf; src.loop = true;
+      // loopEnd = the source's TRUE length, for a bed that is compressed. AAC pads the last packet,
+      // and Chrome hands back a buffer ~17 ms longer than the master — silence spliced in at every
+      // seam, once a loop, on the title screen. Trimming the seam is what keeps the loop seamless.
+      // Zero (the default, and every uncompressed bed) leaves the whole buffer in play.
+      if (loopEnd) src.loopEnd = loopEnd;
       const hp = ac.createBiquadFilter(); hp.type = 'highpass'; hp.frequency.value = lowcut;
       // start SILENT if it was ducked while loading: a multi-megabyte file takes seconds to fetch
       // and decode, and a player who taps straight through the picker would otherwise have the
@@ -101,13 +106,18 @@ function loopBed(file, lowcut, vol) {
     })
     .catch(() => beds.delete(file)); // failed start (decode/network) can retry next call
 }
-export const ambient = () => loopBed('tennis-ambient-loop', 500, 0.035);  // whole-scene atmosphere, from first tap
-export const zombieMusic = () => loopBed('zombie-mode', 800, 0.2);         // background music once splatter kicks in
+export const ambient = () => loopBed('tennis-ambient-loop.wav', 500, 0.035);  // whole-scene atmosphere, from first tap
+export const zombieMusic = () => loopBed('zombie-mode.wav', 800, 0.2);         // background music once splatter kicks in
 // Menu theme: the splash, the court picker, the death summary. Barely highpassed — this one is
 // MUSIC, not an atmosphere bed, so the low end is the point. Started at boot so it is already
 // running by the time the title is on screen; on a phone the autoplay policy holds the context
 // suspended until the first tap, and it becomes audible then (see loopBed).
-export const menuMusic = () => loopBed('background-music', 30, 0.5);
+// AAC, not WAV: 48 s of stereo music is 8.3 MB as a WAV and this one downloads on every page load,
+// before the player has decided to play anything. 768 KB encoded, and the master is exactly 48.000 s
+// — which is the loopEnd, because the decoded buffer is NOT (measured 48.0174 s in Chrome; see the
+// padding note in loopBed). Re-encode the file and you must re-measure that number:
+//   fetch(f).then(r=>r.arrayBuffer()).then(a=>new AudioContext().decodeAudioData(a)).then(b=>b.duration)
+export const menuMusic = () => loopBed('background-music.m4a', 30, 0.5, 48);
 
 // duck a bed to silence (out=true) or back to its base level over `secs` — the sudden-death duel mutes the music
 function fadeBed(file, out, secs = 0.7) {
@@ -119,10 +129,10 @@ function fadeBed(file, out, secs = 0.7) {
   b.g.gain.setValueAtTime(b.g.gain.value, t); // anchor at current level so a mid-fade toggle stays smooth
   b.g.gain.linearRampToValueAtTime(out ? 0 : b.vol, t + secs);
 }
-export const zombieDuck = out => fadeBed('zombie-mode', out);
+export const zombieDuck = out => fadeBed('zombie-mode.wav', out); // key must match loopBed's, filename and all
 // The menu theme is never stopped, only faded — the buffer is already decoded, so fading it back up
 // on the death screen costs nothing and can't miss its cue waiting on a re-fetch.
-export const menuDuck = out => fadeBed('background-music', out);
+export const menuDuck = out => fadeBed('background-music.m4a', out);
 
 let sysVoice = null;
 export function say(text, delay = 0) { // fallback when a recorded umpire line is missing
diff --git a/index.html b/index.html
index 9e3b0ab..32bf864 100644
--- a/index.html
+++ b/index.html
@@ -117,6 +117,6 @@
     <div id="courts"><h2>CHOOSE YOUR COURT</h2></div>
   </div>
 </div>
-<script type="module" src="main.js?v=84"></script>
+<script type="module" src="main.js?v=86"></script>
 </body>
 </html>