From 7abba26948b5f625d61a7c5c260b92fe15ff8a20 Mon Sep 17 00:00:00 2001
From: "prompt.ac/@jeffrey" <mail@aesthetic.computer>
Date: Sun, 16 Aug 2026 12:54:46 -0400
Subject: [PATCH] =?UTF-8?q?The=20room's=20true=20silence=20bug,=20caught?=
 =?UTF-8?q?=20by=20the=20new=20meters:=20the=20tap=20aggregate=20runs=20on?=
 =?UTF-8?q?=20the=20OUTPUT=20DEVICE's=20clock=20(96=20kHz=20on=20neo)=20wh?=
 =?UTF-8?q?ile=20the=20tap=20claims=2048=20kHz,=20so=20captured=20audio=20?=
 =?UTF-8?q?was=20wrapped=20at=20the=20wrong=20rate=20=E2=80=94=20half=20pi?=
 =?UTF-8?q?tch=20had=20it=20ever=20played=20=E2=80=94=20and=20the=20presen?=
 =?UTF-8?q?tation=20clock=20raced=202=C3=97=20real=20time,=20scheduling=20?=
 =?UTF-8?q?every=20chunk=20for=20a=20future=20the=20render=20window=20neve?=
 =?UTF-8?q?r=20reaches=20(receiver=20windows=20showed=20+1=20s=20drifting?=
 =?UTF-8?q?=20to=20+16=20s=20in=2015=20s=20while=20both=20ends=20read=20's?=
 =?UTF-8?q?ignal=20present').=20The=20tap=20now=20trusts=20the=20aggregate?=
 =?UTF-8?q?'s=20nominal=20rate=20over=20its=20own=20claim,=20and=20the=20s?=
 =?UTF-8?q?ender=20resyncs=20its=20presentation=20clock=20with=20a=20fresh?=
 =?UTF-8?q?=20session=20if=20it=20ever=20drifts=20a=20second=20from=20wall?=
 =?UTF-8?q?-clock=20+=20latency?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 .../Sources/ACMacAudio/ProcessAudioTap.swift   | 18 ++++++++++++++++++
 .../Sources/ACMacAudio/RoomSender.swift        | 13 +++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/slab/macos-audio/Sources/ACMacAudio/ProcessAudioTap.swift b/slab/macos-audio/Sources/ACMacAudio/ProcessAudioTap.swift
index 703f4a9792..0ecbbf3413 100644
--- a/slab/macos-audio/Sources/ACMacAudio/ProcessAudioTap.swift
+++ b/slab/macos-audio/Sources/ACMacAudio/ProcessAudioTap.swift
@@ -77,6 +77,24 @@ public final class ACProcessAudioTap: @unchecked Sendable {
             ]
             status = AudioHardwareCreateAggregateDevice(aggregateDescription as CFDictionary, &aggregateID)
             guard status == noErr else { throw ACAudioRoomError.coreAudio("Create tap aggregate", status) }
+            // The IOProc runs on the AGGREGATE's clock (its main subdevice is
+            // the current output device) and drift compensation delivers the
+            // tap's samples AT THAT RATE. On a 96 kHz interface, a tap that
+            // claims 48 kHz would otherwise have its buffers wrapped and
+            // paced as 48 kHz: audio at the wrong pitch and a presentation
+            // clock racing 2× real time, so receivers chase chunks scheduled
+            // for a future that never arrives. Trust the aggregate's rate.
+            if let aggregateRate = try? Self.read(aggregateID,
+                                                  selector: kAudioDevicePropertyNominalSampleRate,
+                                                  defaultValue: Double(0)),
+               aggregateRate > 0, abs(aggregateRate - format.sampleRate) > 1 {
+                var corrected = stream
+                corrected.mSampleRate = aggregateRate
+                if let correctedFormat = AVAudioFormat(streamDescription: &corrected) {
+                    self.format = correctedFormat
+                    onLog?("tap delivers at aggregate rate \(Int(aggregateRate)) Hz (tap claimed \(Int(format.sampleRate)))")
+                }
+            }
             self.handler = handler
             status = AudioDeviceCreateIOProcIDWithBlock(&ioProcID, aggregateID, queue) {
                 [weak self] _, inputData, _, _, _ in
diff --git a/slab/macos-audio/Sources/ACMacAudio/RoomSender.swift b/slab/macos-audio/Sources/ACMacAudio/RoomSender.swift
index bfd15bdf1b..e211bffadb 100644
--- a/slab/macos-audio/Sources/ACMacAudio/RoomSender.swift
+++ b/slab/macos-audio/Sources/ACMacAudio/RoomSender.swift
@@ -173,6 +173,19 @@ public final class ACAudioRoomSender: @unchecked Sendable {
         }
         lastAudioNanos = now
 
+        // Insurance against pacing bugs (a wrong input rate, device quirks):
+        // if the presentation clock drifts more than a second from
+        // wall-clock + latency, resync with a fresh session rather than
+        // keep scheduling audio for a time that never comes.
+        let target = now + configuration.latencyMilliseconds * 1_000_000
+        let drift = Int64(bitPattern: nextPresentationNanos &- target)
+        if abs(drift) > 1_000_000_000 {
+            log(String(format: "presentation clock drifted %+.1f s — resyncing", Double(drift) / 1e9))
+            session = UInt32.random(in: 1...UInt32.max)
+            sequence = 0
+            nextPresentationNanos = target
+        }
+
         var offset = 0
         let total = Int(output.frameLength)
         while offset < total {
-- 
2.51.2