[feat] add video adaptation preference setting

apps/ios/CrossDeskMobile/Bridge/CrossDeskRTCBridge.h

@@ -35,6 +35,12 @@ typedef NS_ENUM(NSInteger, CrossDeskPointerAction) {
   CrossDeskPointerActionMiddleUp,
 };
 
+typedef NS_ENUM(NSInteger, CrossDeskVideoAdaptationPolicy) {
+  CrossDeskVideoAdaptationPolicyFrameRatePriority = 0,
+  CrossDeskVideoAdaptationPolicyQualityPriority,
+  CrossDeskVideoAdaptationPolicyBalanced,
+};
+
 @class CrossDeskRTCBridge;
 
 @protocol CrossDeskRTCBridgeDelegate <NSObject>
@@ -96,6 +102,7 @@ typedef NS_ENUM(NSInteger, CrossDeskPointerAction) {
                        turnPort:(NSInteger)turnPort
                      enableSRTP:(BOOL)enableSRTP;
 - (void)setHardwareAccelerationEnabled:(BOOL)enabled;
+- (void)setVideoAdaptationPolicy:(CrossDeskVideoAdaptationPolicy)policy;
 - (void)requestPresenceForRemoteIDs:(NSArray<NSString *> *)remoteIDs
     NS_SWIFT_NAME(requestPresence(remoteIDs:));
 

apps/ios/CrossDeskMobile/Bridge/CrossDeskRTCBridge.mm

@@ -72,6 +72,8 @@ struct RTCState {
   int turn_port = 0;
   bool enable_srtp = false;
   bool hardware_acceleration = true;
+  VideoDegradationPreference video_adaptation_policy =
+      VideoDegradationPreference::MaintainResolution;
   bool identity_ready = false;
   bool identity_recovery_attempted = false;
   std::string identity_with_password;
@@ -334,8 +336,7 @@ Params MakeParams(const RTCState &state, const std::string &user_id,
   params.video_content_type = VideoContentType::ScreenContent;
   params.video_quality = VideoQuality::QualityHigh;
   params.video_frame_rate = 60;
-  params.video_degradation_preference =
-      VideoDegradationPreference::MaintainResolution;
+  params.video_degradation_preference = state.video_adaptation_policy;
   params.on_receive_video_buffer = nullptr;
   params.on_receive_audio_buffer = OnAudioBuffer;
   params.on_receive_data_buffer = OnDataBuffer;
@@ -496,6 +497,26 @@ Params MakeParams(const RTCState &state, const std::string &user_id,
   });
 }
 
+- (void)setVideoAdaptationPolicy:(CrossDeskVideoAdaptationPolicy)policy {
+  dispatch_async(_rtcQueue, ^{
+    switch (policy) {
+      case CrossDeskVideoAdaptationPolicyFrameRatePriority:
+        self->_state->video_adaptation_policy =
+            VideoDegradationPreference::MaintainFrameRate;
+        break;
+      case CrossDeskVideoAdaptationPolicyBalanced:
+        self->_state->video_adaptation_policy =
+            VideoDegradationPreference::Balanced;
+        break;
+      case CrossDeskVideoAdaptationPolicyQualityPriority:
+      default:
+        self->_state->video_adaptation_policy =
+            VideoDegradationPreference::MaintainResolution;
+        break;
+    }
+  });
+}
+
 - (void)requestPresenceForRemoteIDs:(NSArray<NSString *> *)remoteIDs {
   NSArray<NSString *> *owned_ids = [remoteIDs copy];
   dispatch_async(_rtcQueue, ^{

apps/ios/CrossDeskMobile/ContentView.swift

@@ -689,6 +689,22 @@ private struct ServerSettingsView: View {
                         .font(.caption)
                         .foregroundStyle(.tertiary)
                 }
+                Section("画面偏好") {
+                    Picker("偏好模式", selection: $session.videoAdaptationPolicy) {
+                        ForEach(VideoAdaptationPolicy.allCases) { policy in
+                            Text(policy.title).tag(policy)
+                        }
+                    }
+                    .pickerStyle(.segmented)
+
+                    Text(session.videoAdaptationPolicy.detail)
+                        .font(.footnote)
+                        .foregroundStyle(.secondary)
+
+                    Text("修改后从下一次连接开始生效。")
+                        .font(.caption)
+                        .foregroundStyle(.tertiary)
+                }
                 Section("服务器") {
                     TextField("信令服务器", text: $session.signalHost)
                         .textInputAutocapitalization(.never)

apps/ios/CrossDeskMobile/RemoteSessionModel.swift

@@ -79,6 +79,55 @@ enum VideoCodecMode: String, CaseIterable, Identifiable {
     }
 }
 
+enum VideoAdaptationPolicy: String, CaseIterable, Identifiable {
+    case frameRatePriority
+    case qualityPriority
+    case balanced
+
+    private static let defaultsKey = "crossdesk.mobile.video-adaptation-policy"
+
+    var id: String { rawValue }
+
+    var title: String {
+        switch self {
+        case .frameRatePriority: return "帧率优先"
+        case .qualityPriority: return "画质优先"
+        case .balanced: return "平衡"
+        }
+    }
+
+    var detail: String {
+        switch self {
+        case .frameRatePriority:
+            return "优先保持画面流畅，带宽或编码压力较大时会更积极地降低分辨率。"
+        case .qualityPriority:
+            return "始终保持较高分辨率，带宽不足时通过降低帧率来保证画面清晰度。"
+        case .balanced:
+            return "兼顾清晰度和流畅度，只在持续压力下逐步降低分辨率。"
+        }
+    }
+
+    var bridgeValue: CrossDeskVideoAdaptationPolicy {
+        switch self {
+        case .frameRatePriority: return .frameRatePriority
+        case .qualityPriority: return .qualityPriority
+        case .balanced: return .balanced
+        }
+    }
+
+    static var saved: VideoAdaptationPolicy {
+        guard let rawValue = UserDefaults.standard.string(forKey: defaultsKey),
+              let policy = VideoAdaptationPolicy(rawValue: rawValue) else {
+            return .qualityPriority
+        }
+        return policy
+    }
+
+    func save() {
+        UserDefaults.standard.set(rawValue, forKey: Self.defaultsKey)
+    }
+}
+
 private struct RemoteVideoFrame {
     let pixelBuffer: CVPixelBuffer
     let encodedSize: CGSize
@@ -317,6 +366,9 @@ final class RemoteSessionModel: NSObject, ObservableObject, CrossDeskRTCBridgeDe
     @Published var videoCodecMode = VideoCodecMode.saved {
         didSet { videoCodecMode.save() }
     }
+    @Published var videoAdaptationPolicy = VideoAdaptationPolicy.saved {
+        didSet { videoAdaptationPolicy.save() }
+    }
     @Published var remoteID = ""
     @Published var password = ""
     @Published private(set) var signalStatus = "正在连接信令服务"
@@ -381,6 +433,7 @@ final class RemoteSessionModel: NSObject, ObservableObject, CrossDeskRTCBridgeDe
             return
         }
         bridge.setHardwareAccelerationEnabled(videoCodecMode == .hardware)
+        bridge.setVideoAdaptationPolicy(videoAdaptationPolicy.bridgeValue)
         bridge.configure(withSignalHost: signalHost,
                          signalPort: signal,
                          turnPort: turn,