From 3e39fcb30f03c32746e8c2908633f06e79e5cf89 Mon Sep 17 00:00:00 2001
From: Ricardo <ricardo@yonkolevel.com>
Date: Tue, 5 May 2026 23:06:54 +0100
Subject: [PATCH] fix(ios): configure AVAudioSession before engine init to
 prevent buffer mismatch

iOS defaults to AVAudioSessionCategorySoloAmbient with a system-chosen buffer
size (~4096 frames on device). Elementary's runtime is initialized with a fixed
block size of 512, causing a mismatch that produces garbage audio (audible as a
low-frequency square wave) immediately on app launch.

Fix: set AVAudioSessionCategoryPlayback with MixWithOthers and AllowBluetoothA2DP,
request a 512-frame preferred buffer duration, activate the session before creating
AVAudioEngine, then derive the actual block size from session.IOBufferDuration so
the runtime always matches what the engine delivers per callback.
---
 ios/Elementary.mm | 29 +++++++++++++++++++++++++++--
 1 file changed, 27 insertions(+), 2 deletions(-)

diff --git a/ios/Elementary.mm b/ios/Elementary.mm
index 6a2b501..0de3332 100644
--- a/ios/Elementary.mm
+++ b/ios/Elementary.mm
@@ -20,6 +20,27 @@ - (instancetype)init
     _sharedInstance = self;
     self.loadedResources = [[NSMutableSet alloc] init];
 
+    // Configure session before engine: iOS default (SoloAmbient, ~4096-frame buffers)
+    // mismatches Elementary's block size and produces garbage audio on launch.
+    NSError *sessionError;
+    AVAudioSession *session = [AVAudioSession sharedInstance];
+    [session setCategory:AVAudioSessionCategoryPlayback
+                    mode:AVAudioSessionModeDefault
+                 options:AVAudioSessionCategoryOptionMixWithOthers |
+                         AVAudioSessionCategoryOptionAllowBluetoothA2DP
+                   error:&sessionError];
+    if (sessionError) {
+      NSLog(@"[Elementary] Failed to set audio session category: %@", sessionError);
+    }
+    [session setPreferredIOBufferDuration:(512.0 / 48000.0) error:&sessionError];
+    if (sessionError) {
+      NSLog(@"[Elementary] Failed to set preferred IO buffer duration: %@", sessionError);
+    }
+    [session setActive:YES error:&sessionError];
+    if (sessionError) {
+      NSLog(@"[Elementary] Failed to activate audio session: %@", sessionError);
+    }
+
     self.audioEngine = [[AVAudioEngine alloc] init];
 
     AVAudioFormat *outputFormat = [self.audioEngine.outputNode outputFormatForBus:0];
@@ -30,7 +51,8 @@ - (instancetype)init
     const float **inputBuffer = (const float **)calloc(numOutputChannels, sizeof(float *));
     float **outputBuffer = (float **)malloc(numOutputChannels * sizeof(float *));
 
-    NSLog(@"[Elementary] Init: %d output channels, sampleRate=%.0f", numOutputChannels, outputFormat.sampleRate);
+    NSLog(@"[Elementary] Init: %d output channels, sampleRate=%.0f, IOBufferDuration=%.4fs",
+          numOutputChannels, outputFormat.sampleRate, session.IOBufferDuration);
 
     AVAudioSourceNode *sourceNode = [[AVAudioSourceNode alloc] initWithRenderBlock:^OSStatus(
             BOOL * _Nonnull isSilence,
@@ -82,7 +104,10 @@ - (instancetype)init
       return nil;
     }
 
-    int bufferSize = 512;
+    // Use granted IOBufferDuration — iOS may not honor the preferred value exactly.
+    int bufferSize = (int)round(outputFormat.sampleRate * session.IOBufferDuration);
+    if (bufferSize <= 0 || bufferSize > 4096) bufferSize = 512; // safety fallback
+    NSLog(@"[Elementary] Runtime block size: %d frames", bufferSize);
     self.runtime = std::make_shared<elem::Runtime<float>>(outputFormat.sampleRate, bufferSize);
 
     [[NSNotificationCenter defaultCenter] addObserver:self