fix: only allow alpha channel toggle when toggle is supported

BetterCapture/Model/SettingsStore.swift

@@ -25,6 +25,26 @@ enum VideoCodec: String, CaseIterable, Identifiable {
             return false
         }
     }
+
+    /// Whether alpha channel is always enabled (cannot be disabled)
+    var alwaysHasAlpha: Bool {
+        switch self {
+        case .proRes4444:
+            return true
+        case .hevc, .h264, .proRes422:
+            return false
+        }
+    }
+
+    /// Whether alpha channel can be toggled by the user
+    var canToggleAlpha: Bool {
+        switch self {
+        case .hevc:
+            return true
+        case .h264, .proRes422, .proRes4444:
+            return false
+        }
+    }
 }
 
 /// Container format for output files
@@ -86,10 +106,15 @@ final class SettingsStore {
         }
         set {
             videoCodecRaw = newValue.rawValue
-            // Reset alpha channel setting if the new codec doesn't support it
-            if !newValue.supportsAlphaChannel {
+            // Set alpha channel based on codec capabilities
+            if newValue.alwaysHasAlpha {
+                // ProRes 4444 always has alpha
+                captureAlphaChannel = true
+            } else if !newValue.supportsAlphaChannel {
+                // H.264 and ProRes 422 never have alpha
                 captureAlphaChannel = false
             }
+            // HEVC can toggle alpha, so leave it as-is
         }
     }
 

BetterCapture/View/MenuBarSettingsView.swift

@@ -51,25 +51,27 @@ struct MenuBarDivider: View {
 struct MenuBarToggle: View {
     let name: String
     @Binding var isOn: Bool
+    var isDisabled: Bool = false
     @State private var isHovered = false
 
     var body: some View {
         HStack {
             Text(name)
                 .font(.system(size: 13, weight: .medium))
-                .foregroundStyle(.primary)
+                .foregroundStyle(isDisabled ? .secondary : .primary)
             Spacer()
             Toggle("", isOn: $isOn)
                 .toggleStyle(.switch)
                 .tint(.blue)
                 .scaleEffect(0.8)
+                .disabled(isDisabled)
         }
         .padding(.horizontal, 12)
         .padding(.vertical, 4)
         .contentShape(.rect)
         .background(
             RoundedRectangle(cornerRadius: 4)
-                .fill(isHovered ? .gray.opacity(0.1) : .clear)
+                .fill(isHovered && !isDisabled ? .gray.opacity(0.1) : .clear)
                 .padding(.horizontal, 4)
         )
         .onHover { hovering in
@@ -421,10 +423,12 @@ struct VideoSettingsSection: View {
                 options: ContainerFormat.allCases.map { ($0, $0.rawValue.uppercased()) }
             )
 
-            // Alpha Channel Toggle (only for supported codecs)
-            if settings.videoCodec.supportsAlphaChannel {
-                MenuBarToggle(name: "Capture Alpha Channel", isOn: $settings.captureAlphaChannel)
-            }
+            // Alpha Channel Toggle (always visible, but disabled for non-toggleable codecs)
+            MenuBarToggle(
+                name: "Capture Alpha Channel",
+                isOn: $settings.captureAlphaChannel,
+                isDisabled: !settings.videoCodec.canToggleAlpha
+            )
         }
     }
 }

BetterCapture/View/SettingsView.swift

@@ -34,6 +34,17 @@ struct SettingsView: View {
 struct VideoSettingsView: View {
     @Bindable var settings: SettingsStore
 
+    private var alphaChannelHelpText: String {
+        switch settings.videoCodec {
+        case .proRes4444:
+            return "ProRes 4444 always includes alpha channel support"
+        case .hevc:
+            return "Enable transparency support for HEVC"
+        case .h264, .proRes422:
+            return "Alpha channel not supported by this codec"
+        }
+    }
+
     var body: some View {
         Form {
             Section("Recording") {
@@ -56,11 +67,10 @@ struct VideoSettingsView: View {
                 }
             }
 
-            if settings.videoCodec.supportsAlphaChannel {
-                Section("Advanced") {
-                    Toggle("Capture Alpha Channel", isOn: $settings.captureAlphaChannel)
-                        .help("Enable transparency support (requires HEVC or ProRes 4444)")
-                }
+            Section("Advanced") {
+                Toggle("Capture Alpha Channel", isOn: $settings.captureAlphaChannel)
+                    .disabled(!settings.videoCodec.canToggleAlpha)
+                    .help(alphaChannelHelpText)
             }
         }
         .formStyle(.grouped)