Improve iOS voice stability and user audio controls

src/VoiceCat.Audio/AdaptivePcmBuffer.cs

@@ -28,7 +28,7 @@ public sealed class AdaptivePcmBuffer
         get => Volatile.Read(ref targetFrames) * 1000 / SampleRate;
         set
         {
-            if (value is not (20 or 40 or 60)) throw new ArgumentOutOfRangeException(nameof(value));
+            if (value is not (20 or 40 or 60 or 120)) throw new ArgumentOutOfRangeException(nameof(value));
             Volatile.Write(ref targetFrames, value * SampleRate / 1000);
         }
     }

src/VoiceCat.Core/ClientMediaTransport.cs

@@ -48,16 +48,26 @@ internal sealed class ClientMediaTransport : IAsyncDisposable
         {
             while (!stop.IsCancellationRequested)
             {
-                if (Environment.TickCount64 >= nextKeepalive)
+                try
                 {
-                    if (!bound.Task.IsCompleted) socket.Send(binding, SocketFlags.None);
-                    socket.Send(keepalive, SocketFlags.None);
-                    nextKeepalive = Environment.TickCount64 + (bound.Task.IsCompleted ? 5000 : 250);
+                    if (Environment.TickCount64 >= nextKeepalive)
+                    {
+                        if (!bound.Task.IsCompleted) socket.Send(binding, SocketFlags.None);
+                        socket.Send(keepalive, SocketFlags.None);
+                        nextKeepalive = Environment.TickCount64 + (bound.Task.IsCompleted ? 5000 : 250);
+                    }
+                    while (packets.TryRead(plain, out VoiceFrameHeader header, out int length))
+                    {
+                        int size = crypto.Encryptor.Encrypt(header, plain.AsSpan(0, length), packet);
+                        socket.Send(packet.AsSpan(0, size), SocketFlags.None);
+                    }
                 }
-                while (packets.TryRead(plain, out VoiceFrameHeader header, out int length))
+                catch (SocketException exception) when (IsTransientNetworkError(exception))
                 {
-                    int size = crypto.Encryptor.Encrypt(header, plain.AsSpan(0, length), packet);
-                    socket.Send(packet.AsSpan(0, size), SocketFlags.None);
+                    // iOS can briefly lose its UDP route while Wi-Fi and cellular switch.
+                    // Keep the sender and socket alive so the next route can carry media.
+                    nextKeepalive = 0;
+                    Thread.Sleep(100);
                 }
                 Thread.Sleep(1);
             }
@@ -77,6 +87,8 @@ internal sealed class ClientMediaTransport : IAsyncDisposable
                 int length;
                 try { length = await socket.ReceiveAsync(packet, SocketFlags.None, stop.Token).ConfigureAwait(false); }
                 catch (SocketException exception) when (exception.SocketErrorCode is SocketError.ConnectionReset or SocketError.MessageSize) { continue; }
+                catch (SocketException exception) when (IsTransientNetworkError(exception))
+                { await Task.Delay(100, stop.Token).ConfigureAwait(false); continue; }
                 if (!VoiceFrameHeader.TryRead(packet.AsSpan(0, length), out var candidate)) continue;
                 if (candidate.Type == MediaFrameType.Keepalive && length == VoiceFrameHeader.Size) { bound.TrySetResult(); continue; }
                 if (candidate.Type != MediaFrameType.Voice || candidate.Codec != 0 ||
@@ -89,6 +101,10 @@ internal sealed class ClientMediaTransport : IAsyncDisposable
         finally { bound.TrySetCanceled(); stop.Cancel(); }
     }
 
+    private static bool IsTransientNetworkError(SocketException exception) => exception.SocketErrorCode is
+        SocketError.NetworkDown or SocketError.NetworkUnreachable or SocketError.HostUnreachable or
+        SocketError.AddressNotAvailable or SocketError.NotConnected or SocketError.ConnectionReset;
+
     public async ValueTask DisposeAsync()
     {
         stop.Cancel(); socket.Dispose();