Add tvOS A/V sync diagnostics on its own settings page

Surface audio-delay (±10/±100 ms) and video-sync-mode controls behind an
"A/V Sync" navigation row in Advanced settings rather than inline, keeping the
Advanced page uncluttered. Audio delay applies live to the running MPV
instance; sync mode takes effect on next playback.

Yattee/Views/Settings/AVSyncDiagnosticsView.swift

@@ -0,0 +1,128 @@
+//
+//  AVSyncDiagnosticsView.swift
+//  Yattee
+//
+//  tvOS A/V sync debugging controls, pushed as its own page from Advanced settings.
+//  - Audio Delay: shifts MPV's `audio-delay` to compensate for fixed HDMI/AVR
+//    output pipeline latency. Applies live to a running MPV instance.
+//  - Video Sync Mode: A/B between `display-vdrop` (default), `display-resample`,
+//    and `audio` modes. Takes effect on next playback start.
+//
+//  The whole screen is tvOS-only because MPV is the tvOS backend and pipeline
+//  latency only differs there; iOS/macOS use the same MPV code path but
+//  happen to balance pipeline lag.
+//
+
+#if os(tvOS)
+import SwiftUI
+
+struct AVSyncDiagnosticsView: View {
+    @Bindable var settings: SettingsManager
+    @Environment(\.appEnvironment) private var appEnvironment
+
+    private let minDelayMs: Double = -500
+    private let maxDelayMs: Double = 500
+    private let stepMs: Double = 10
+
+    var body: some View {
+        SettingsFormContainer {
+            SettingsFormSection(
+                footer: "settings.playback.tvSyncDiagnostics.footer"
+            ) {
+            // Current value as a non-interactive row — tvOS Form rows can't
+            // host multiple focusable controls, so we surface the value here
+            // and put each control on its own row below.
+            HStack {
+                Label(
+                    String(localized: "settings.playback.tvAudioDelay"),
+                    systemImage: "speaker.wave.2.bubble"
+                )
+                Spacer()
+                Text(String(format: "%+.0f ms", settings.tvAudioDelayMs))
+                    .monospacedDigit()
+                    .foregroundStyle(.secondary)
+            }
+
+            // Coarse steps (±100 ms) first so the user can land near the
+            // right value fast, then fine (±10 ms) to dial it in.
+            Button {
+                adjust(by: -100)
+            } label: {
+                Label(
+                    String(localized: "settings.playback.tvAudioDelay.minus100"),
+                    systemImage: "gobackward.minus"
+                )
+            }
+            .disabled(settings.tvAudioDelayMs <= minDelayMs)
+
+            Button {
+                adjust(by: -stepMs)
+            } label: {
+                Label(
+                    String(localized: "settings.playback.tvAudioDelay.minus10"),
+                    systemImage: "minus"
+                )
+            }
+            .disabled(settings.tvAudioDelayMs <= minDelayMs)
+
+            Button {
+                adjust(by: stepMs)
+            } label: {
+                Label(
+                    String(localized: "settings.playback.tvAudioDelay.plus10"),
+                    systemImage: "plus"
+                )
+            }
+            .disabled(settings.tvAudioDelayMs >= maxDelayMs)
+
+            Button {
+                adjust(by: 100)
+            } label: {
+                Label(
+                    String(localized: "settings.playback.tvAudioDelay.plus100"),
+                    systemImage: "goforward.plus"
+                )
+            }
+            .disabled(settings.tvAudioDelayMs >= maxDelayMs)
+
+            Button(role: .destructive) {
+                set(to: 0)
+            } label: {
+                Label(
+                    String(localized: "settings.playback.tvAudioDelay.reset"),
+                    systemImage: "arrow.counterclockwise"
+                )
+            }
+            .disabled(settings.tvAudioDelayMs == 0)
+
+            PlatformMenuPicker(
+                String(localized: "settings.playback.tvVideoSyncMode"),
+                selection: $settings.tvVideoSyncMode
+            ) {
+                    ForEach(TVVideoSyncMode.allCases, id: \.self) { mode in
+                        Text(mode.displayName).tag(mode)
+                    }
+                }
+            }
+        }
+    }
+
+    private func adjust(by delta: Double) {
+        let next = (settings.tvAudioDelayMs + delta).clamped(to: minDelayMs...maxDelayMs)
+        set(to: next)
+    }
+
+    private func set(to value: Double) {
+        settings.tvAudioDelayMs = value
+        if let mpvBackend = appEnvironment?.playerService.currentBackend as? MPVBackend {
+            mpvBackend.updateAudioDelay(milliseconds: value)
+        }
+    }
+}
+
+private extension Comparable {
+    func clamped(to range: ClosedRange<Self>) -> Self {
+        min(max(self, range.lowerBound), range.upperBound)
+    }
+}
+#endif

Yattee/Views/Settings/AdvancedSettingsView.swift

@@ -32,6 +32,9 @@ struct AdvancedSettingsView: View {
             #endif
             streamDetailsSection
             mpvSection
+            #if os(tvOS)
+            avSyncSection
+            #endif
             settingsSection
             #if !os(tvOS)
             downloadsStorageSection
@@ -230,6 +233,26 @@ struct AdvancedSettingsView: View {
         }
     }
 
+    #if os(tvOS)
+    @ViewBuilder
+    private var avSyncSection: some View {
+        if let settings = appEnvironment?.settingsManager {
+            SettingsFormSection {
+                NavigationLink {
+                    TVSidebarDetailContainer(
+                        systemImage: "wave.3.right",
+                        title: String(localized: "settings.playback.tvSyncDiagnostics.header")
+                    ) {
+                        AVSyncDiagnosticsView(settings: settings)
+                    }
+                } label: {
+                    Label(String(localized: "settings.playback.tvSyncDiagnostics.row"), systemImage: "wave.3.right")
+                }
+            }
+        }
+    }
+    #endif
+
     private static let mpvBufferOptions: [Double] = [1.0, 2.0, 3.0, 4.0, 5.0]
 
     private func formatBufferOption(_ seconds: Double) -> String {