Keep managed iOS audio active in background

clients/apple/dotnet/VoiceCat.iOS/AppModel.cs

@@ -32,6 +32,7 @@ internal sealed class AppModel
     private uint restoreChannel;
     private bool restoreMuted;
     private bool restoreDeafened;
+    private bool backgrounded;
 
     internal event Action? Changed;
     internal event Action<ServerIdentityChallenge>? IdentityRequested;
@@ -44,6 +45,7 @@ internal sealed class AppModel
     internal bool IsConnecting { get; private set; }
     internal bool VoiceJoined => microphoneStream != 0;
     internal bool ScreenSharing => broadcast?.IsActive == true;
+    internal bool IsBackgrounded => backgrounded;
     internal float MicrophoneLevel { get; private set; }
     internal string Status { get; private set; } = "Not connected";
     internal uint CurrentChannelId { get; private set; }
@@ -55,6 +57,27 @@ internal sealed class AppModel
     internal void Load() { profiles.Clear(); profiles.AddRange(storage.LoadProfiles()); settings.Load(); IosAudioRouter.Shared.Load(); Notify(); }
     internal void Save() { storage.SaveProfiles(profiles); settings.Save(); }
 
+    internal void DidEnterBackground()
+    {
+        backgrounded = true; Save();
+        // Do not stop or rebuild AVAudioEngine here. With the `audio` background mode and an
+        // active PlayAndRecord session, capture, playback, media UDP, and screen-ring draining
+        // remain live while the scene is backgrounded or the device is locked.
+    }
+
+    internal void WillEnterForeground()
+    {
+        backgrounded = false;
+        IosAudioRouter.Shared.Recover("foreground");
+    }
+
+    internal void DidBecomeActive()
+    {
+        backgrounded = false;
+        IosAudioRouter.Shared.EnsureAudio("active scene");
+        Notify();
+    }
+
     internal void UpsertProfile(ServerProfile profile, string? password)
     {
         int index = profiles.FindIndex(item => item.Id == profile.Id);
@@ -186,6 +209,17 @@ internal sealed class AppModel
         microphoneStream = stream.StreamId; IosAudioEngine.Shared.StartMicrophone(stream.StreamId, channels); feedback.Play(SoundEvent.VoiceOn); Notify();
     }
 
+    internal void ToggleScreenAudio()
+    {
+        if (!OperatingSystem.IsIOSVersionAtLeast(27)) throw new PlatformNotSupportedException("Use the ReplayKit broadcast picker on this iOS version.");
+        if (ScreenSharing) { IosScreenCapture.Stop(); broadcast?.RequestStop(); }
+        else
+        {
+            if (!IsConnected || CurrentChannelId == 0) throw new InvalidOperationException("Connect and join a channel before sharing screen audio.");
+            IosScreenCapture.Present();
+        }
+    }
+
     internal void SetSelfAudio(bool muted, bool deafened) { client?.SetSelfAudioState(muted, deafened); Notify(); }
     internal void SetPushToTalk(bool active)
     {

clients/apple/dotnet/VoiceCat.iOS/BroadcastAudioPump.cs

@@ -13,6 +13,7 @@ internal sealed class BroadcastAudioPump : IAsyncDisposable
     private VoiceCatClient? client;
     private uint streamId;
     private bool active;
+    private int generation;
     private readonly short[] scratch = new short[Frame * 2];
 
     internal event Action? Changed;
@@ -43,7 +44,13 @@ internal sealed class BroadcastAudioPump : IAsyncDisposable
         VoiceCatClient owner = client ?? throw new IOException("Client disconnected.");
         if (streamId == 0)
         {
+            int startGeneration = Volatile.Read(ref generation);
             StreamInfo stream = await owner.StartStreamAsync(StreamKind.StreamScreenAudio, "Screen audio", 2, token).ConfigureAwait(false);
+            if (startGeneration != Volatile.Read(ref generation) || view.ReadUInt32(16) == 0 || !ReferenceEquals(client, owner))
+            {
+                try { owner.StopStream(stream.StreamId); } catch (Exception exception) when (exception is IOException or InvalidOperationException) { }
+                return;
+            }
             streamId = stream.StreamId; view.Write(32, view.ReadUInt64(24)); SetActive(true);
         }
         ulong write = view.ReadUInt64(24), read = view.ReadUInt64(32);
@@ -67,10 +74,12 @@ internal sealed class BroadcastAudioPump : IAsyncDisposable
         try { client.StopStream(id); } catch (Exception exception) when (exception is IOException or InvalidOperationException) { }
     }
 
+    internal void RequestStop() { Interlocked.Increment(ref generation); SetActive(false); }
+
     private void SetActive(bool value) { if (active == value) return; active = value; Changed?.Invoke(); }
 
     public async ValueTask DisposeAsync()
     {
-        stop.Cancel(); try { await worker.ConfigureAwait(false); } catch (OperationCanceledException) { } StopStream(); SetActive(false); stop.Dispose();
+        stop.Cancel(); Interlocked.Increment(ref generation); try { await worker.ConfigureAwait(false); } catch (OperationCanceledException) { } StopStream(); SetActive(false); stop.Dispose();
     }
 }

clients/apple/dotnet/VoiceCat.iOS/IosAudioEngine.cs

@@ -43,6 +43,11 @@ internal sealed class IosAudioEngine
 
     internal void StopMicrophone() { microphoneStream = 0; Rebuild(); }
     internal void Reconfigure() { if (IsConnected) Rebuild(); }
+    internal bool EnsureRunning()
+    {
+        if (!IsConnected || engine?.Running == true) return true;
+        Rebuild(); return engine?.Running == true;
+    }
 
     private void Rebuild()
     {

clients/apple/dotnet/VoiceCat.iOS/IosAudioRouter.cs

@@ -33,9 +33,9 @@ internal sealed class IosAudioRouter
 
     private IosAudioRouter()
     {
-        NSNotificationCenter.DefaultCenter.AddObserver(AVAudioSession.RouteChangeNotification, _ => Recover());
+        NSNotificationCenter.DefaultCenter.AddObserver(AVAudioSession.RouteChangeNotification, HandleRouteChange);
         NSNotificationCenter.DefaultCenter.AddObserver(AVAudioSession.InterruptionNotification, HandleInterruption);
-        NSNotificationCenter.DefaultCenter.AddObserver(AVAudioSession.MediaServicesWereResetNotification, _ => Recover());
+        NSNotificationCenter.DefaultCenter.AddObserver(AVAudioSession.MediaServicesWereResetNotification, _ => Recover("media services reset"));
     }
 
     internal void Load()
@@ -131,10 +131,38 @@ internal sealed class IosAudioRouter
 
     private void Set(string key, string? value) { if (value is null) defaults.RemoveObject(key); else defaults.SetString(value, key); }
     internal void Deactivate() => AVAudioSession.SharedInstance().SetActive(false, AVAudioSessionSetActiveOptions.NotifyOthersOnDeactivation, out _);
-    private void Recover() { RefreshRoutes(); if (IosAudioEngine.Shared.IsConnected) UIApplication.SharedApplication.BeginInvokeOnMainThread(IosAudioEngine.Shared.Reconfigure); }
+    internal void EnsureAudio(string reason)
+    {
+        if (!IosAudioEngine.Shared.IsConnected) return;
+        try { IosAudioEngine.Shared.EnsureRunning(); }
+        catch (Exception exception) { System.Diagnostics.Debug.WriteLine($"Audio recovery ({reason}) failed: {exception}"); }
+    }
+
+    internal void Recover(string reason)
+    {
+        RefreshRoutes();
+        if (!IosAudioEngine.Shared.IsConnected) return;
+        UIApplication.SharedApplication.BeginInvokeOnMainThread(() =>
+        {
+            try { IosAudioEngine.Shared.Reconfigure(); }
+            catch (Exception exception) { System.Diagnostics.Debug.WriteLine($"Audio recovery ({reason}) failed: {exception}"); }
+        });
+    }
+    private void HandleRouteChange(NSNotification note)
+    {
+        NSNumber? value = note.UserInfo?[new NSString("AVAudioSessionRouteChangeReasonKey")] as NSNumber;
+        AVAudioSessionRouteChangeReason reason = (AVAudioSessionRouteChangeReason)(value?.UInt32Value ?? 0);
+        RefreshRoutes();
+        if (reason is AVAudioSessionRouteChangeReason.CategoryChange
+            or AVAudioSessionRouteChangeReason.Override
+            or AVAudioSessionRouteChangeReason.RouteConfigurationChange)
+            return;
+        Recover($"route change ({reason})");
+    }
     private void HandleInterruption(NSNotification note)
     {
         NSNumber? type = note.UserInfo?[new NSString("AVAudioSessionInterruptionTypeKey")] as NSNumber;
-        if ((AVAudioSessionInterruptionType)(type?.UInt32Value ?? 0) == AVAudioSessionInterruptionType.Ended) Recover();
+        AVAudioSessionInterruptionType interruption = (AVAudioSessionInterruptionType)(type?.UInt32Value ?? 0);
+        if (interruption == AVAudioSessionInterruptionType.Ended) Recover("interruption ended");
     }
 }

clients/apple/dotnet/VoiceCat.iOS/IosScreenCapture.cs

@@ -11,9 +11,11 @@ internal static partial class IosScreenCapture
         NSUrl? root = NSFileManager.DefaultManager.GetContainerUrl(IosConstants.AppGroup);
         if (root?.Path is null) throw new InvalidOperationException("The VoiceCat App Group is unavailable.");
         string path = Path.Combine(root.Path, "voicecat", "broadcast_audio.ring"); Directory.CreateDirectory(Path.GetDirectoryName(path)!);
-        if (Available() == 0) throw new InvalidOperationException("Screen audio sharing is unavailable on this device."); PresentNative(path);
+        if (!IsAvailable) throw new InvalidOperationException("Screen audio sharing is unavailable on this device."); PresentNative(path);
     }
 
+    internal static bool IsAvailable => OperatingSystem.IsIOSVersionAtLeast(27) && Available() != 0;
+
     [LibraryImport("__Internal", EntryPoint = "vc_ios_screen_capture_available")]
     private static partial int Available();
     [LibraryImport("__Internal", EntryPoint = "vc_ios_screen_capture_present", StringMarshalling = StringMarshalling.Utf8)]

clients/apple/dotnet/VoiceCat.iOS/SceneDelegate.cs

@@ -18,5 +18,11 @@ internal sealed class SceneDelegate : UIResponder, IUIWindowSceneDelegate
     }
 
     [Export("sceneDidEnterBackground:")]
-    public void DidEnterBackground(UIScene scene) => AppModel.Shared.Save();
+    public void DidEnterBackground(UIScene scene) => AppModel.Shared.DidEnterBackground();
+
+    [Export("sceneWillEnterForeground:")]
+    public void WillEnterForeground(UIScene scene) => AppModel.Shared.WillEnterForeground();
+
+    [Export("sceneDidBecomeActive:")]
+    public void DidBecomeActive(UIScene scene) => AppModel.Shared.DidBecomeActive();
 }

clients/apple/dotnet/VoiceCat.iOS/SettingsController.cs

@@ -21,7 +21,7 @@ internal sealed class SettingsController : UITableViewController
         UITableViewCell cell = tableView.DequeueReusableCell("setting", path); cell.AccessoryView = null; cell.Accessory = UITableViewCellAccessory.None;
         string title = path.Section switch
         {
-            0 => path.Row switch { 0 => "Audio preset", 1 => "Speaker output", 2 => "Advanced audio", _ => "Share screen audio" },
+            0 => path.Row switch { 0 => "Audio preset", 1 => "Speaker output", 2 => "Advanced audio", _ => model.ScreenSharing ? "Stop sharing screen audio" : "Share screen audio" },
             1 => path.Row switch { 0 => "Input mode", 1 => $"VAD threshold: {model.Settings.VadThreshold:0.000}", 2 => $"Microphone volume: {model.Settings.InputGain:P0}", _ => "Microphone noise reduction" },
             2 => path.Row switch { 0 => "Event sounds", 1 => $"Sound volume: {model.Settings.EventVolume:P0}", 2 => "Speak events", 3 => "Own voice activity sounds", _ => "Push-to-talk cue" },
             3 => "Manage accounts", _ => path.Row == 0 ? "Disconnect" : "VoiceCat 0.0.1"
@@ -54,7 +54,7 @@ internal sealed class SettingsController : UITableViewController
     private void Slider(string title, float minimum, float maximum, float current, Action<float> changed) { var slider = new UISlider(new CoreGraphics.CGRect(16, 48, 238, 28)) { MinValue = minimum, MaxValue = maximum, Value = current, AccessibilityLabel = title }; UIAlertController alert = UIAlertController.Create(title, null, UIAlertControllerStyle.Alert); alert.View!.AddSubview(slider); alert.AddAction(UIAlertAction.Create("Cancel", UIAlertActionStyle.Cancel, null)); alert.AddAction(UIAlertAction.Create("Apply", UIAlertActionStyle.Default, _ => changed(slider.Value))); PresentViewController(alert, true, null); }
     private void ShowScreenSharing()
     {
-        if (OperatingSystem.IsIOSVersionAtLeast(27)) { IosScreenCapture.Present(); return; }
+        if (OperatingSystem.IsIOSVersionAtLeast(27)) { model.ToggleScreenAudio(); return; }
 #pragma warning disable CA1422
         var picker = new RPSystemBroadcastPickerView(new CoreGraphics.CGRect(0, 0, 60, 60)) { PreferredExtension = IosConstants.BroadcastExtension, ShowsMicrophoneButton = false };
 #pragma warning restore CA1422

clients/apple/dotnet/VoiceCat.iOS/native/ios_screen_capture.m

@@ -70,11 +70,12 @@ static SCContentSharingPicker *VCSharedPicker(void) {
     SCContentSharingPickerConfiguration *configuration = [configurationClass new];
     if (!picker || !configuration) return;
     configuration.showsMicrophoneControl = NO; configuration.showsCameraControl = NO; picker.defaultConfiguration = configuration;
-    [picker addObserver:self]; picker.active = YES; [picker presentPickerUsingContentStyle:SCShareableContentStyleDisplay];
+    [picker removeObserver:self]; [picker addObserver:self]; picker.active = YES; [picker presentPickerUsingContentStyle:SCShareableContentStyleDisplay];
 }
 
 - (void)stop {
-    [self.stream stopCaptureWithCompletionHandler:^(__unused NSError *error) {}]; self.stream = nil; [self setRingActive:NO];
+    [self.stream stopCaptureWithCompletionHandler:^(__unused NSError *error) {}]; self.stream = nil;
+    SCContentSharingPicker *picker = VCSharedPicker(); [picker removeObserver:self]; picker.active = NO; [self setRingActive:NO];
 }
 
 - (void)contentSharingPicker:(SCContentSharingPicker *)picker didUpdateWithFilter:(SCContentFilter *)filter forStream:(SCStream *)stream API_AVAILABLE(ios(27.0)) {