initial prototype: synced mp3 playback

2026-02-10 12:08:04 +01:00
commit 4b14d06bc8
30 changed files with 1784 additions and 0 deletions
--- a/.gitignore
+++ b/.gitignore
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+				INFOPLIST_FILE = CoopRunning/Info.plist;
+				IPHONEOS_DEPLOYMENT_TARGET = 26.0;
+				LOCALIZED_STRING_SWIFT_SYMBOLS = YES;
+				MARKETING_VERSION = 0.1.0;
+				MTL_ENABLE_DEBUG_INFO = NO;
+				MTL_FAST_MATH = YES;
+				PRODUCT_BUNDLE_IDENTIFIER = de.felixfoertsch.cooprunning;
+				PRODUCT_NAME = "$(TARGET_NAME)";
+				PROVISIONING_PROFILE_SPECIFIER = "";
+				SDKROOT = iphoneos;
+				STRING_CATALOG_GENERATE_SYMBOLS = YES;
+				SWIFT_COMPILATION_MODE = wholemodule;
+				SWIFT_OPTIMIZATION_LEVEL = "-O";
+				SWIFT_STRING_CATALOGS = YES;
+				SWIFT_VERSION = 5.9;
+				TARGETED_DEVICE_FAMILY = 1;
+			};
+			name = Release;
+		};
+/* End XCBuildConfiguration section */
+
+/* Begin XCConfigurationList section */
+		2322A6CDF4FC2AE59DD780B1 /* Build configuration list for PBXNativeTarget "CoopRunningTests" */ = {
+			isa = XCConfigurationList;
+			buildConfigurations = (
+				2A934AD016F05C8A94BF4DA8 /* Debug */,
+				84DDC04A355E486EE89AC7F8 /* Release */,
+			);
+			defaultConfigurationIsVisible = 0;
+			defaultConfigurationName = Debug;
+		};
+		3BCFE323CCC2757AAFD6F452 /* Build configuration list for PBXProject "CoopRunning" */ = {
+			isa = XCConfigurationList;
+			buildConfigurations = (
+				DE756993C972E7F7EDB4067D /* Debug */,
+				F630219557065594A62AFA33 /* Release */,
+			);
+			defaultConfigurationIsVisible = 0;
+			defaultConfigurationName = Debug;
+		};
+		5E860FBA956CBCBD03474441 /* Build configuration list for PBXNativeTarget "CoopRunning" */ = {
+			isa = XCConfigurationList;
+			buildConfigurations = (
+				B10B4E0B66978D394F8DD3C9 /* Debug */,
+				5FDDE7CAF9D800EFEF79CEAB /* Release */,
+			);
+			defaultConfigurationIsVisible = 0;
+			defaultConfigurationName = Debug;
+		};
+/* End XCConfigurationList section */
+	};
+	rootObject = 45108C7370BA21AEC5D4E16A /* Project object */;
+}
--- a/CoopRunning.xcodeproj/xcshareddata/xcschemes/CoopRunning.xcscheme
+++ b/CoopRunning.xcodeproj/xcshareddata/xcschemes/CoopRunning.xcscheme
@@ -0,0 +1,102 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<Scheme
+   LastUpgradeVersion = "1430"
+   version = "1.7">
+   <BuildAction
+      parallelizeBuildables = "YES"
+      buildImplicitDependencies = "YES"
+      runPostActionsOnFailure = "NO">
+      <BuildActionEntries>
+         <BuildActionEntry
+            buildForTesting = "YES"
+            buildForRunning = "YES"
+            buildForProfiling = "YES"
+            buildForArchiving = "YES"
+            buildForAnalyzing = "YES">
+            <BuildableReference
+               BuildableIdentifier = "primary"
+               BlueprintIdentifier = "6D8086D1FAEE224EF0BE91DB"
+               BuildableName = "CoopRunning.app"
+               BlueprintName = "CoopRunning"
+               ReferencedContainer = "container:CoopRunning.xcodeproj">
+            </BuildableReference>
+         </BuildActionEntry>
+      </BuildActionEntries>
+   </BuildAction>
+   <TestAction
+      buildConfiguration = "Debug"
+      selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
+      selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
+      shouldUseLaunchSchemeArgsEnv = "YES"
+      onlyGenerateCoverageForSpecifiedTargets = "NO">
+      <MacroExpansion>
+         <BuildableReference
+            BuildableIdentifier = "primary"
+            BlueprintIdentifier = "6D8086D1FAEE224EF0BE91DB"
+            BuildableName = "CoopRunning.app"
+            BlueprintName = "CoopRunning"
+            ReferencedContainer = "container:CoopRunning.xcodeproj">
+         </BuildableReference>
+      </MacroExpansion>
+      <Testables>
+         <TestableReference
+            skipped = "NO"
+            parallelizable = "NO">
+            <BuildableReference
+               BuildableIdentifier = "primary"
+               BlueprintIdentifier = "7176FDC3954B3226DB5DEE48"
+               BuildableName = "CoopRunningTests.xctest"
+               BlueprintName = "CoopRunningTests"
+               ReferencedContainer = "container:CoopRunning.xcodeproj">
+            </BuildableReference>
+         </TestableReference>
+      </Testables>
+      <CommandLineArguments>
+      </CommandLineArguments>
+   </TestAction>
+   <LaunchAction
+      buildConfiguration = "Debug"
+      selectedDebuggerIdentifier = "Xcode.DebuggerFoundation.Debugger.LLDB"
+      selectedLauncherIdentifier = "Xcode.DebuggerFoundation.Launcher.LLDB"
+      launchStyle = "0"
+      useCustomWorkingDirectory = "NO"
+      ignoresPersistentStateOnLaunch = "NO"
+      debugDocumentVersioning = "YES"
+      debugServiceExtension = "internal"
+      allowLocationSimulation = "YES">
+      <BuildableProductRunnable
+         runnableDebuggingMode = "0">
+         <BuildableReference
+            BuildableIdentifier = "primary"
+            BlueprintIdentifier = "6D8086D1FAEE224EF0BE91DB"
+            BuildableName = "CoopRunning.app"
+            BlueprintName = "CoopRunning"
+            ReferencedContainer = "container:CoopRunning.xcodeproj">
+         </BuildableReference>
+      </BuildableProductRunnable>
+   </LaunchAction>
+   <ProfileAction
+      buildConfiguration = "Release"
+      shouldUseLaunchSchemeArgsEnv = "YES"
+      savedToolIdentifier = ""
+      useCustomWorkingDirectory = "NO"
+      debugDocumentVersioning = "YES">
+      <BuildableProductRunnable
+         runnableDebuggingMode = "0">
+         <BuildableReference
+            BuildableIdentifier = "primary"
+            BlueprintIdentifier = "6D8086D1FAEE224EF0BE91DB"
+            BuildableName = "CoopRunning.app"
+            BlueprintName = "CoopRunning"
+            ReferencedContainer = "container:CoopRunning.xcodeproj">
+         </BuildableReference>
+      </BuildableProductRunnable>
+   </ProfileAction>
+   <AnalyzeAction
+      buildConfiguration = "Debug">
+   </AnalyzeAction>
+   <ArchiveAction
+      buildConfiguration = "Release"
+      revealArchiveInOrganizer = "YES">
+   </ArchiveAction>
+</Scheme>
--- a/CoopRunning.xcworkspace/contents.xcworkspacedata
+++ b/CoopRunning.xcworkspace/contents.xcworkspacedata
@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<Workspace
+   version = "1.0">
+   <FileRef
+      location = "group:CoopRunning.xcodeproj">
+   </FileRef>
+</Workspace>
--- a/CoopRunning/AppModel.swift
+++ b/CoopRunning/AppModel.swift
@@ -0,0 +1,242 @@
+import Foundation
+import Combine
+
+final class AppModel: ObservableObject {
+    @Published var role: SessionRole = .idle
+    @Published var isConnected: Bool = false
+    @Published var peers: [PeerInfo] = []
+    @Published var statusText: String = "Not connected"
+
+    @Published var library: [LocalTrack] = []
+    @Published var selectedTrack: LocalTrack? = nil
+
+    @Published var isPlaying: Bool = false
+    @Published var playbackPosition: TimeInterval = 0
+
+    private let audio = AudioPlayerController()
+    private let session = PeerSession()
+    private var cancellables: Set<AnyCancellable> = []
+    private var driftTimer: Timer?
+    private var pendingTrackNames: [String: String] = [:]
+    private var pendingPlay: SyncPlayPayload? = nil
+
+    init() {
+        Task { [weak self] in
+            guard let self else { return }
+            let loaded = await LocalTrack.loadLibrary()
+            await MainActor.run {
+                self.library = loaded
+                self.selectedTrack = loaded.first
+            }
+        }
+
+        session.$peers
+            .receive(on: DispatchQueue.main)
+            .assign(to: &$peers)
+
+        session.$isConnected
+            .receive(on: DispatchQueue.main)
+            .sink { [weak self] connected in
+                self?.isConnected = connected
+                if connected && self?.role == .host {
+                    self?.syncNow()
+                }
+            }
+            .store(in: &cancellables)
+
+        session.$statusText
+            .receive(on: DispatchQueue.main)
+            .assign(to: &$statusText)
+
+        audio.$isPlaying
+            .receive(on: DispatchQueue.main)
+            .assign(to: &$isPlaying)
+
+        audio.$playbackPosition
+            .receive(on: DispatchQueue.main)
+            .assign(to: &$playbackPosition)
+
+        session.onMessage = { [weak self] message in
+            self?.handle(message: message)
+        }
+        session.onReceiveResource = { [weak self] name, url in
+            self?.handleResource(name: name, url: url)
+        }
+    }
+
+    func host() {
+        role = .host
+        session.startHosting()
+    }
+
+    func join() {
+        role = .peer
+        session.startJoining()
+    }
+
+    func stop() {
+        role = .idle
+        session.stop()
+        audio.stop()
+        stopDriftTimer()
+    }
+
+    func importTrack(url: URL) throws {
+        Task { [weak self] in
+            guard let self else { return }
+            do {
+                let newTrack = try await LocalTrack.importTrack(from: url)
+                let loaded = await LocalTrack.loadLibrary()
+                await MainActor.run {
+                    self.library = loaded
+                    self.selectedTrack = newTrack
+                }
+            } catch {
+                await MainActor.run {
+                    self.statusText = "Import failed: \(error.localizedDescription)"
+                }
+            }
+        }
+    }
+
+    func select(track: LocalTrack) {
+        selectedTrack = track
+    }
+
+    func togglePlay() {
+        guard let track = selectedTrack else { return }
+
+        if role == .host {
+            if audio.isPlaying {
+                audio.pause()
+                session.broadcast(.pause)
+                stopDriftTimer()
+            } else {
+                // Schedule a shared future start time to align peers.
+                let startDelay: TimeInterval = 2.0
+                let startUptime = SyncClock.uptime() + startDelay
+                let payload = SyncPlayPayload(
+                    trackID: track.id.uuidString,
+                    startUptime: startUptime,
+                    startPosition: audio.playbackPosition
+                )
+                session.broadcast(.play(payload))
+                audio.play(track: track, atUptime: startUptime, startPosition: audio.playbackPosition)
+                startDriftTimer()
+            }
+        }
+    }
+
+    func seek(to position: TimeInterval) {
+        guard selectedTrack != nil else { return }
+        audio.seek(to: position)
+
+        if role == .host {
+            session.broadcast(.seek(position))
+        }
+    }
+
+    func syncNow() {
+        guard role == .host else { return }
+        session.broadcast(.syncRequest(SyncClock.uptime()))
+    }
+
+    func sendTrackToPeers() {
+        guard role == .host, let track = selectedTrack else { return }
+        session.sendTrack(track)
+    }
+
+    private func handle(message: SessionMessage) {
+        switch message {
+        case .hello:
+            return
+        case .libraryRequest:
+            return
+        case .trackInfo(let info):
+            pendingTrackNames[info.trackID] = info.displayName
+        case .trackRequest(let trackID):
+            guard role == .host else { return }
+            if let track = library.first(where: { $0.id.uuidString == trackID }) {
+                session.sendTrack(track)
+            }
+        case .play(let payload):
+            guard role == .peer else { return }
+            if let track = library.first(where: { $0.id.uuidString == payload.trackID }) {
+                selectedTrack = track
+                let localStart = SyncClock.convert(hostUptime: payload.startUptime)
+                audio.play(track: track, atUptime: localStart, startPosition: payload.startPosition)
+            } else {
+                pendingPlay = payload
+                session.broadcast(.trackRequest(payload.trackID))
+                statusText = "Missing track. Requested from host."
+            }
+        case .pause:
+            guard role == .peer else { return }
+            audio.pause()
+        case .seek(let position):
+            guard role == .peer else { return }
+            audio.seek(to: position)
+        case .syncRequest(let hostUptime):
+            guard role == .peer else { return }
+            session.reply(.syncResponse(hostUptime: hostUptime, peerUptime: SyncClock.uptime()))
+        case .syncResponse(let hostUptime, let peerUptime):
+            guard role == .host else { return }
+            session.updateOffset(hostUptime: hostUptime, peerUptime: peerUptime)
+        case .driftCorrection(let position, let hostUptime):
+            guard role == .peer else { return }
+            audio.correctDrift(targetPosition: position, hostUptime: hostUptime)
+        }
+    }
+
+    private func handleResource(name: String, url: URL) {
+        guard name.hasPrefix("track:") else { return }
+        let trackID = String(name.dropFirst("track:".count))
+        let displayName = pendingTrackNames[trackID] ?? "Track"
+        Task { [weak self] in
+            guard let self else { return }
+            do {
+                let newTrack = try await LocalTrack.importReceivedTrack(from: url, trackID: trackID, displayName: displayName)
+                let loaded = await LocalTrack.loadLibrary()
+                await MainActor.run {
+                    self.library = loaded
+                    self.selectedTrack = newTrack
+                    self.statusText = "Received track: \(displayName)"
+                    if let pending = self.pendingPlay, pending.trackID == trackID {
+                        let localStart = SyncClock.convert(hostUptime: pending.startUptime)
+                        self.audio.play(track: newTrack, atUptime: localStart, startPosition: pending.startPosition)
+                        self.pendingPlay = nil
+                    }
+                }
+            } catch {
+                await MainActor.run {
+                    self.statusText = "Import failed: \(error.localizedDescription)"
+                }
+            }
+        }
+    }
+
+    private func startDriftTimer() {
+        stopDriftTimer()
+        driftTimer = Timer.scheduledTimer(withTimeInterval: 2.0, repeats: true) { [weak self] _ in
+            guard let self, self.role == .host else { return }
+            let payload = (self.audio.playbackPosition, SyncClock.uptime())
+            self.session.broadcast(.driftCorrection(position: payload.0, hostUptime: payload.1))
+        }
+    }
+
+    private func stopDriftTimer() {
+        driftTimer?.invalidate()
+        driftTimer = nil
+    }
+}
+
+enum SessionRole: String {
+    case idle
+    case host
+    case peer
+}
+
+struct PeerInfo: Identifiable, Hashable {
+    let id: String
+    let name: String
+}
--- a/CoopRunning/Assets.xcassets/AppIcon.appiconset/Contents.json
+++ b/CoopRunning/Assets.xcassets/AppIcon.appiconset/Contents.json
@@ -0,0 +1,74 @@
+{
+  "images" : [
+    {
+      "filename" : "Icon-20@2x.png",
+      "idiom" : "iphone",
+      "scale" : "2x",
+      "size" : "20x20"
+    },
+    {
+      "filename" : "Icon-20@3x.png",
+      "idiom" : "iphone",
+      "scale" : "3x",
+      "size" : "20x20"
+    },
+    {
+      "filename" : "Icon-29@2x.png",
+      "idiom" : "iphone",
+      "scale" : "2x",
+      "size" : "29x29"
+    },
+    {
+      "filename" : "Icon-29@3x.png",
+      "idiom" : "iphone",
+      "scale" : "3x",
+      "size" : "29x29"
+    },
+    {
+      "filename" : "Icon-40@2x.png",
+      "idiom" : "iphone",
+      "scale" : "2x",
+      "size" : "40x40"
+    },
+    {
+      "filename" : "Icon-40@3x.png",
+      "idiom" : "iphone",
+      "scale" : "3x",
+      "size" : "40x40"
+    },
+    {
+      "filename" : "Icon-60@2x.png",
+      "idiom" : "iphone",
+      "scale" : "2x",
+      "size" : "60x60"
+    },
+    {
+      "filename" : "Icon-60@3x.png",
+      "idiom" : "iphone",
+      "scale" : "3x",
+      "size" : "60x60"
+    },
+    {
+      "filename" : "Icon-76@2x.png",
+      "idiom" : "ipad",
+      "scale" : "2x",
+      "size" : "76x76"
+    },
+    {
+      "filename" : "Icon-83.5@2x.png",
+      "idiom" : "ipad",
+      "scale" : "2x",
+      "size" : "83.5x83.5"
+    },
+    {
+      "filename" : "Icon-1024.png",
+      "idiom" : "ios-marketing",
+      "scale" : "1x",
+      "size" : "1024x1024"
+    }
+  ],
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}
--- a/CoopRunning/Assets.xcassets/AppIcon.appiconset/Icon-1024.png
+++ b/CoopRunning/Assets.xcassets/AppIcon.appiconset/Icon-1024.png
--- a/CoopRunning/Assets.xcassets/AppIcon.appiconset/Icon-20@2x.png
+++ b/CoopRunning/Assets.xcassets/AppIcon.appiconset/Icon-20@2x.png
--- a/CoopRunning/Assets.xcassets/AppIcon.appiconset/Icon-20@3x.png
+++ b/CoopRunning/Assets.xcassets/AppIcon.appiconset/Icon-20@3x.png
--- a/CoopRunning/Assets.xcassets/AppIcon.appiconset/Icon-29@2x.png
+++ b/CoopRunning/Assets.xcassets/AppIcon.appiconset/Icon-29@2x.png
--- a/CoopRunning/Assets.xcassets/AppIcon.appiconset/Icon-29@3x.png
+++ b/CoopRunning/Assets.xcassets/AppIcon.appiconset/Icon-29@3x.png
--- a/CoopRunning/Assets.xcassets/AppIcon.appiconset/Icon-40@2x.png
+++ b/CoopRunning/Assets.xcassets/AppIcon.appiconset/Icon-40@2x.png
--- a/CoopRunning/Assets.xcassets/AppIcon.appiconset/Icon-40@3x.png
+++ b/CoopRunning/Assets.xcassets/AppIcon.appiconset/Icon-40@3x.png
--- a/CoopRunning/Assets.xcassets/AppIcon.appiconset/Icon-60@2x.png
+++ b/CoopRunning/Assets.xcassets/AppIcon.appiconset/Icon-60@2x.png
--- a/CoopRunning/Assets.xcassets/AppIcon.appiconset/Icon-60@3x.png
+++ b/CoopRunning/Assets.xcassets/AppIcon.appiconset/Icon-60@3x.png
--- a/CoopRunning/Assets.xcassets/AppIcon.appiconset/Icon-76@2x.png
+++ b/CoopRunning/Assets.xcassets/AppIcon.appiconset/Icon-76@2x.png
--- a/CoopRunning/Assets.xcassets/AppIcon.appiconset/Icon-83.5@2x.png
+++ b/CoopRunning/Assets.xcassets/AppIcon.appiconset/Icon-83.5@2x.png
--- a/CoopRunning/Assets.xcassets/Contents.json
+++ b/CoopRunning/Assets.xcassets/Contents.json
@@ -0,0 +1,6 @@
+{
+  "info" : {
+    "author" : "xcode",
+    "version" : 1
+  }
+}
--- a/CoopRunning/AudioPlayerController.swift
+++ b/CoopRunning/AudioPlayerController.swift
@@ -0,0 +1,129 @@
+import Foundation
+import AVFoundation
+import Darwin
+
+final class AudioPlayerController: NSObject, ObservableObject {
+    @Published private(set) var isPlaying: Bool = false
+    @Published private(set) var playbackPosition: TimeInterval = 0
+
+    private let engine = AVAudioEngine()
+    private let playerNode = AVAudioPlayerNode()
+    private var audioFile: AVAudioFile?
+    private var progressTimer: Timer?
+    private var didConfigureSession = false
+
+    private var currentTrack: LocalTrack?
+    private var scheduleStartPosition: TimeInterval = 0
+
+    override init() {
+        super.init()
+        engine.attach(playerNode)
+        engine.connect(playerNode, to: engine.mainMixerNode, format: nil)
+    }
+
+    func play(track: LocalTrack, atUptime startUptime: TimeInterval, startPosition: TimeInterval) {
+        configureAudioSessionIfNeeded()
+
+        do {
+            let file = try AVAudioFile(forReading: track.url)
+            audioFile = file
+            currentTrack = track
+            scheduleStartPosition = startPosition
+
+            let startFrame = AVAudioFramePosition(startPosition * file.fileFormat.sampleRate)
+            let totalFrames = file.length
+            let framesLeft = max(AVAudioFrameCount(totalFrames - startFrame), 0)
+
+            if !engine.isRunning {
+                try engine.start()
+            }
+
+            playerNode.stop()
+            playerNode.scheduleSegment(
+                file,
+                startingFrame: startFrame,
+                frameCount: framesLeft,
+                at: AVAudioTime(hostTime: hostTime(forUptime: startUptime))
+            ) { [weak self] in
+                DispatchQueue.main.async {
+                    self?.isPlaying = false
+                    self?.stopProgressTimer()
+                }
+            }
+
+            if !playerNode.isPlaying {
+                playerNode.play()
+            }
+
+            isPlaying = true
+            startProgressTimer()
+        } catch {
+            isPlaying = false
+        }
+    }
+
+    func pause() {
+        playerNode.pause()
+        isPlaying = false
+        stopProgressTimer()
+    }
+
+    func stop() {
+        playerNode.stop()
+        isPlaying = false
+        playbackPosition = 0
+        stopProgressTimer()
+    }
+
+    func seek(to position: TimeInterval) {
+        guard let track = currentTrack else { return }
+        play(track: track, atUptime: SyncClock.uptime() + 0.1, startPosition: position)
+    }
+
+    func correctDrift(targetPosition: TimeInterval, hostUptime: TimeInterval) {
+        guard let track = currentTrack else { return }
+        let targetNow = SyncClock.convert(hostUptime: hostUptime)
+        let expectedPosition = targetPosition + (SyncClock.uptime() - targetNow)
+        let drift = expectedPosition - playbackPosition
+        if abs(drift) > 0.15 {
+            play(track: track, atUptime: SyncClock.uptime() + 0.1, startPosition: expectedPosition)
+        }
+    }
+
+    private func startProgressTimer() {
+        stopProgressTimer()
+        progressTimer = Timer.scheduledTimer(withTimeInterval: 0.25, repeats: true) { [weak self] _ in
+            guard let self else { return }
+            if let nodeTime = self.playerNode.lastRenderTime,
+               let playerTime = self.playerNode.playerTime(forNodeTime: nodeTime) {
+                let seconds = Double(playerTime.sampleTime) / playerTime.sampleRate
+                self.playbackPosition = self.scheduleStartPosition + seconds
+                self.isPlaying = self.playerNode.isPlaying
+            }
+        }
+    }
+
+    private func stopProgressTimer() {
+        progressTimer?.invalidate()
+        progressTimer = nil
+    }
+
+    private func configureAudioSessionIfNeeded() {
+        guard !didConfigureSession else { return }
+        do {
+            let session = AVAudioSession.sharedInstance()
+            try session.setCategory(.playback, mode: .default)
+            try session.setActive(true)
+            didConfigureSession = true
+        } catch {
+            didConfigureSession = false
+        }
+    }
+
+    private func hostTime(forUptime startUptime: TimeInterval) -> UInt64 {
+        let nowUptime = SyncClock.uptime()
+        let delay = max(0, startUptime - nowUptime)
+        let hostDelay = AVAudioTime.hostTime(forSeconds: delay)
+        return mach_absolute_time() + hostDelay
+    }
+}
--- a/CoopRunning/ContentView.swift
+++ b/CoopRunning/ContentView.swift
@@ -0,0 +1,160 @@
+import SwiftUI
+import UniformTypeIdentifiers
+
+struct ContentView: View {
+    @EnvironmentObject private var appModel: AppModel
+    @State private var isImporting = false
+
+    var body: some View {
+        ZStack {
+            LinearGradient(
+                colors: [Color.blue.opacity(0.25), Color.cyan.opacity(0.18), Color.mint.opacity(0.12)],
+                startPoint: .topLeading,
+                endPoint: .bottomTrailing
+            )
+            .ignoresSafeArea()
+
+            ScrollView {
+                VStack(spacing: 16) {
+                    header
+                    card(roleSection)
+                    card(librarySection)
+                    card(playbackSection)
+                    card(connectionSection)
+                }
+                .padding(20)
+            }
+        }
+        .fileImporter(
+            isPresented: $isImporting,
+            allowedContentTypes: [.mp3, .mpeg4Audio, .audio],
+            allowsMultipleSelection: false
+        ) { result in
+            do {
+                let url = try result.get().first
+                guard let url else { return }
+                try appModel.importTrack(url: url)
+            } catch {
+                appModel.statusText = "Import failed: \(error.localizedDescription)"
+            }
+        }
+    }
+
+    private var header: some View {
+        VStack(spacing: 6) {
+            Text("CoopRunning Sync")
+                .font(.title2).bold()
+            Text(appModel.statusText)
+                .font(.footnote)
+                .foregroundStyle(.secondary)
+        }
+    }
+
+    private var roleSection: some View {
+        HStack(spacing: 12) {
+            Button("Host") { appModel.host() }
+                .buttonStyle(.borderedProminent)
+            Button("Join") { appModel.join() }
+                .buttonStyle(.bordered)
+            Button("Stop") { appModel.stop() }
+                .buttonStyle(.bordered)
+        }
+    }
+
+    private var librarySection: some View {
+        VStack(alignment: .leading, spacing: 8) {
+            HStack {
+                Text("Library")
+                    .font(.headline)
+                Spacer()
+                Button("Import MP3") {
+                    isImporting = true
+                }
+            }
+
+            if appModel.library.isEmpty {
+                Text("No local tracks yet.")
+                    .foregroundStyle(.secondary)
+            } else {
+                Picker("Track", selection: Binding(get: {
+                    appModel.selectedTrack
+                }, set: { newValue in
+                    if let track = newValue { appModel.select(track: track) }
+                })) {
+                    ForEach(appModel.library) { track in
+                        Text(track.displayName).tag(Optional(track))
+                    }
+                }
+                .pickerStyle(.menu)
+            }
+        }
+        .frame(maxWidth: .infinity, alignment: .leading)
+    }
+
+    private var playbackSection: some View {
+        VStack(alignment: .leading, spacing: 8) {
+            Text("Playback")
+                .font(.headline)
+
+            HStack(spacing: 12) {
+                Button(appModel.isPlaying ? "Pause" : "Play") {
+                    appModel.togglePlay()
+                }
+                .buttonStyle(.borderedProminent)
+                .disabled(appModel.selectedTrack == nil || appModel.role != .host)
+
+                Button("Send Track") {
+                    appModel.sendTrackToPeers()
+                }
+                .buttonStyle(.bordered)
+                .disabled(appModel.selectedTrack == nil || appModel.role != .host || !appModel.isConnected)
+
+                Button("Sync Now") {
+                    appModel.syncNow()
+                }
+                .buttonStyle(.bordered)
+                .disabled(appModel.role != .host)
+            }
+
+            HStack {
+                Text("Position")
+                Slider(value: Binding(get: {
+                    appModel.playbackPosition
+                }, set: { newValue in
+                    appModel.seek(to: newValue)
+                }), in: 0...max(appModel.selectedTrack?.duration ?? 1, 1))
+            }
+            .disabled(appModel.selectedTrack == nil || appModel.role != .host)
+        }
+        .frame(maxWidth: .infinity, alignment: .leading)
+    }
+
+    private var connectionSection: some View {
+        VStack(alignment: .leading, spacing: 8) {
+            Text("Peers")
+                .font(.headline)
+
+            if appModel.peers.isEmpty {
+                Text("No peers yet")
+                    .foregroundStyle(.secondary)
+            } else {
+                ForEach(appModel.peers) { peer in
+                    Text(peer.name)
+                        .font(.subheadline)
+                }
+            }
+        }
+        .frame(maxWidth: .infinity, alignment: .leading)
+    }
+
+    private func card<V: View>(_ content: V) -> some View {
+        content
+            .padding(12)
+            .frame(maxWidth: .infinity, alignment: .leading)
+            .background(.thinMaterial, in: RoundedRectangle(cornerRadius: 16, style: .continuous))
+            .overlay(
+                RoundedRectangle(cornerRadius: 16, style: .continuous)
+                    .strokeBorder(Color.white.opacity(0.15))
+            )
+    }
+}
--- a/CoopRunning/CoopRunningApp.swift
+++ b/CoopRunning/CoopRunningApp.swift
@@ -0,0 +1,13 @@
+import SwiftUI
+
+@main
+struct CoopRunningApp: App {
+    @StateObject private var appModel = AppModel()
+
+    var body: some Scene {
+        WindowGroup {
+            ContentView()
+                .environmentObject(appModel)
+        }
+    }
+}
--- a/CoopRunning/Info.plist
+++ b/CoopRunning/Info.plist
@@ -0,0 +1,43 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>CFBundleDevelopmentRegion</key>
+	<string>$(DEVELOPMENT_LANGUAGE)</string>
+	<key>CFBundleDisplayName</key>
+	<string>CoopRunning</string>
+	<key>CFBundleExecutable</key>
+	<string>$(EXECUTABLE_NAME)</string>
+	<key>CFBundleIdentifier</key>
+	<string>$(PRODUCT_BUNDLE_IDENTIFIER)</string>
+	<key>CFBundleInfoDictionaryVersion</key>
+	<string>6.0</string>
+	<key>CFBundleName</key>
+	<string>$(PRODUCT_NAME)</string>
+	<key>CFBundlePackageType</key>
+	<string>APPL</string>
+	<key>CFBundleShortVersionString</key>
+	<string>1.0</string>
+	<key>CFBundleVersion</key>
+	<string>1</string>
+	<key>LSRequiresIPhoneOS</key>
+	<true/>
+	<key>NSBluetoothAlwaysUsageDescription</key>
+	<string>Find nearby runners</string>
+	<key>NSBonjourServices</key>
+	<array>
+		<string>_cooprun-sync._tcp</string>
+	</array>
+	<key>NSLocalNetworkUsageDescription</key>
+	<string>Sync audio with nearby runners</string>
+	<key>UILaunchStoryboardName</key>
+	<string>LaunchScreen</string>
+	<key>UISupportedInterfaceOrientations</key>
+	<array>
+		<string>UIInterfaceOrientationPortrait</string>
+		<string>UIInterfaceOrientationPortraitUpsideDown</string>
+		<string>UIInterfaceOrientationLandscapeLeft</string>
+		<string>UIInterfaceOrientationLandscapeRight</string>
+	</array>
+</dict>
+</plist>
--- a/CoopRunning/LaunchScreen.storyboard
+++ b/CoopRunning/LaunchScreen.storyboard
@@ -0,0 +1,29 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<document type="com.apple.InterfaceBuilder3.CocoaTouch.Storyboard.XIB" version="3.0" toolsVersion="21701" targetRuntime="iOS.CocoaTouch" propertyAccessControl="none" useAutolayout="YES" launchScreen="YES" useTraitCollections="YES" initialViewController="01J-lp-oVM">
+    <device id="retina6_12" orientation="portrait" appearance="light"/>
+    <scenes>
+        <scene sceneID="EHf-IW-A2E">
+            <objects>
+                <viewController id="01J-lp-oVM" sceneMemberID="viewController">
+                    <view key="view" contentMode="scaleToFill" id="Ze5-6b-2t3">
+                        <rect key="frame" x="0.0" y="0.0" width="390" height="844"/>
+                        <subviews>
+                            <label opaque="NO" userInteractionEnabled="NO" contentMode="left" horizontalHuggingPriority="251" verticalHuggingPriority="251" text="CoopRunning" textAlignment="center" lineBreakMode="middleTruncation" baselineAdjustment="alignBaselines" adjustsFontSizeToFit="NO" translatesAutoresizingMaskIntoConstraints="NO" id="1aC-zt-x8B">
+                                <rect key="frame" x="120" y="412" width="150" height="20"/>
+                                <fontDescription key="fontDescription" type="system" pointSize="17" weight="semibold"/>
+                                <color key="textColor" systemColor="labelColor"/>
+                            </label>
+                        </subviews>
+                        <viewLayoutGuide key="safeArea" id="Bcu-3y-fUS"/>
+                        <constraints>
+                            <constraint firstItem="1aC-zt-x8B" firstAttribute="centerX" secondItem="Ze5-6b-2t3" secondAttribute="centerX" id="IhJ-0C-9pW"/>
+                            <constraint firstItem="1aC-zt-x8B" firstAttribute="centerY" secondItem="Ze5-6b-2t3" secondAttribute="centerY" id="iLJ-yt-9u1"/>
+                        </constraints>
+                    </view>
+                </viewController>
+                <placeholder placeholderIdentifier="IBFirstResponder" id="iYj-Kq-Ea1" userLabel="First Responder" sceneMemberID="firstResponder"/>
+            </objects>
+            <point key="canvasLocation" x="52" y="375"/>
+        </scene>
+    </scenes>
+</document>
--- a/CoopRunning/LocalTrack.swift
+++ b/CoopRunning/LocalTrack.swift
@@ -0,0 +1,70 @@
+import Foundation
+import AVFoundation
+
+struct LocalTrack: Identifiable, Hashable {
+    let id: UUID
+    let url: URL
+    let displayName: String
+    let duration: TimeInterval
+
+    static func libraryDirectory() -> URL {
+        let docs = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!
+        let dir = docs.appendingPathComponent("CoopRunning", isDirectory: true)
+        if !FileManager.default.fileExists(atPath: dir.path) {
+            try? FileManager.default.createDirectory(at: dir, withIntermediateDirectories: true)
+        }
+        return dir
+    }
+
+    static func loadLibrary() async -> [LocalTrack] {
+        let dir = libraryDirectory()
+        let urls = (try? FileManager.default.contentsOfDirectory(at: dir, includingPropertiesForKeys: nil)) ?? []
+        var tracks: [LocalTrack] = []
+        for url in urls {
+            let asset = AVURLAsset(url: url)
+            let duration = (try? await asset.load(.duration).seconds) ?? 0
+            let track = LocalTrack(
+                id: UUID(uuidString: url.deletingPathExtension().lastPathComponent) ?? UUID(),
+                url: url,
+                displayName: url.deletingPathExtension().lastPathComponent,
+                duration: duration
+            )
+            tracks.append(track)
+        }
+        return tracks.sorted { $0.displayName.lowercased() < $1.displayName.lowercased() }
+    }
+
+    static func importTrack(from url: URL) async throws -> LocalTrack {
+        let dir = libraryDirectory()
+        let id = UUID()
+        let dest = dir.appendingPathComponent("\(id.uuidString).mp3")
+        let didStart = url.startAccessingSecurityScopedResource()
+        defer {
+            if didStart { url.stopAccessingSecurityScopedResource() }
+        }
+        try FileManager.default.copyItem(at: url, to: dest)
+        let duration = (try? await AVURLAsset(url: dest).load(.duration).seconds) ?? 0
+        return LocalTrack(
+            id: id,
+            url: dest,
+            displayName: url.deletingPathExtension().lastPathComponent,
+            duration: duration
+        )
+    }
+
+    static func importReceivedTrack(from url: URL, trackID: String, displayName: String) async throws -> LocalTrack {
+        let dir = libraryDirectory()
+        let dest = dir.appendingPathComponent("\(trackID).mp3")
+        if FileManager.default.fileExists(atPath: dest.path) {
+            try FileManager.default.removeItem(at: dest)
+        }
+        try FileManager.default.moveItem(at: url, to: dest)
+        let duration = (try? await AVURLAsset(url: dest).load(.duration).seconds) ?? 0
+        return LocalTrack(
+            id: UUID(uuidString: trackID) ?? UUID(),
+            url: dest,
+            displayName: displayName,
+            duration: duration
+        )
+    }
+}
--- a/CoopRunning/PeerSession.swift
+++ b/CoopRunning/PeerSession.swift
@@ -0,0 +1,162 @@
+import Foundation
+import MultipeerConnectivity
+import UIKit
+
+final class PeerSession: NSObject, ObservableObject {
+    @Published private(set) var peers: [PeerInfo] = []
+    @Published private(set) var isConnected: Bool = false
+    @Published private(set) var statusText: String = "Idle"
+
+    var onMessage: ((SessionMessage) -> Void)?
+    var onReceiveResource: ((String, URL) -> Void)?
+
+    private let serviceType = "cooprun-sync"
+    private let myPeerID = MCPeerID(displayName: UIDevice.current.name)
+
+    private var session: MCSession!
+    private var advertiser: MCNearbyServiceAdvertiser?
+    private var browser: MCNearbyServiceBrowser?
+
+    // Host keeps per-peer offsets
+    private var peerOffsets: [MCPeerID: TimeInterval] = [:]
+
+    override init() {
+        super.init()
+        session = MCSession(peer: myPeerID, securityIdentity: nil, encryptionPreference: .required)
+        session.delegate = self
+    }
+
+    func startHosting() {
+        stop()
+        statusText = "Hosting"
+        advertiser = MCNearbyServiceAdvertiser(peer: myPeerID, discoveryInfo: nil, serviceType: serviceType)
+        advertiser?.delegate = self
+        advertiser?.startAdvertisingPeer()
+    }
+
+    func startJoining() {
+        stop()
+        statusText = "Browsing"
+        browser = MCNearbyServiceBrowser(peer: myPeerID, serviceType: serviceType)
+        browser?.delegate = self
+        browser?.startBrowsingForPeers()
+    }
+
+    func stop() {
+        advertiser?.stopAdvertisingPeer()
+        advertiser = nil
+        browser?.stopBrowsingForPeers()
+        browser = nil
+        session.disconnect()
+        peers = []
+        isConnected = false
+        statusText = "Idle"
+        peerOffsets = [:]
+    }
+
+    func broadcast(_ message: SessionMessage) {
+        guard !session.connectedPeers.isEmpty else { return }
+        send(message, to: session.connectedPeers)
+    }
+
+    func reply(_ message: SessionMessage) {
+        guard !session.connectedPeers.isEmpty else { return }
+        send(message, to: session.connectedPeers)
+    }
+
+    func updateOffset(hostUptime: TimeInterval, peerUptime: TimeInterval) {
+        for peer in session.connectedPeers {
+            let offset = hostUptime - peerUptime
+            peerOffsets[peer] = offset
+        }
+    }
+
+    func sendTrack(_ track: LocalTrack) {
+        guard !session.connectedPeers.isEmpty else { return }
+        let info = TrackInfoPayload(trackID: track.id.uuidString, displayName: track.displayName)
+        send(.trackInfo(info), to: session.connectedPeers)
+        for peer in session.connectedPeers {
+            let resourceName = "track:\(track.id.uuidString)"
+            session.sendResource(at: track.url, withName: resourceName, toPeer: peer) { [weak self] error in
+                if let error {
+                    DispatchQueue.main.async {
+                        self?.statusText = "Send track failed: \(error.localizedDescription)"
+                    }
+                }
+            }
+        }
+    }
+
+    private func send(_ message: SessionMessage, to peers: [MCPeerID]) {
+        do {
+            let data = try JSONEncoder().encode(message)
+            try session.send(data, toPeers: peers, with: .reliable)
+        } catch {
+            statusText = "Send failed: \(error.localizedDescription)"
+        }
+    }
+
+    private func handle(_ data: Data, from peerID: MCPeerID) {
+        do {
+            let message = try JSONDecoder().decode(SessionMessage.self, from: data)
+            if case .syncRequest(let hostUptime) = message {
+                let peerUptime = SyncClock.uptime()
+                SyncClock.setHostOffset(hostUptime: hostUptime, peerUptime: peerUptime)
+            }
+            onMessage?(message)
+        } catch {
+            statusText = "Decode failed: \(error.localizedDescription)"
+        }
+    }
+}
+
+extension PeerSession: MCSessionDelegate {
+    func session(_ session: MCSession, peer peerID: MCPeerID, didChange state: MCSessionState) {
+        DispatchQueue.main.async {
+            self.peers = session.connectedPeers.map { PeerInfo(id: $0.displayName, name: $0.displayName) }
+            self.isConnected = !session.connectedPeers.isEmpty
+            switch state {
+            case .connected:
+                self.statusText = "Connected to \(peerID.displayName)"
+                self.send(.hello, to: [peerID])
+            case .connecting:
+                self.statusText = "Connecting to \(peerID.displayName)"
+            case .notConnected:
+                self.statusText = "Disconnected"
+            @unknown default:
+                self.statusText = "Unknown state"
+            }
+        }
+    }
+
+    func session(_ session: MCSession, didReceive data: Data, fromPeer peerID: MCPeerID) {
+        DispatchQueue.main.async {
+            self.handle(data, from: peerID)
+        }
+    }
+
+    func session(_ session: MCSession, didReceive stream: InputStream, withName streamName: String, fromPeer peerID: MCPeerID) {}
+
+    func session(_ session: MCSession, didStartReceivingResourceWithName resourceName: String, fromPeer peerID: MCPeerID, with progress: Progress) {}
+
+    func session(_ session: MCSession, didFinishReceivingResourceWithName resourceName: String, fromPeer peerID: MCPeerID, at localURL: URL?, withError error: Error?) {
+        guard error == nil, let localURL else { return }
+        DispatchQueue.main.async {
+            self.onReceiveResource?(resourceName, localURL)
+        }
+    }
+}
+
+extension PeerSession: MCNearbyServiceAdvertiserDelegate {
+    func advertiser(_ advertiser: MCNearbyServiceAdvertiser, didReceiveInvitationFromPeer peerID: MCPeerID, withContext context: Data?, invitationHandler: @escaping (Bool, MCSession?) -> Void) {
+        invitationHandler(true, session)
+    }
+}
+
+extension PeerSession: MCNearbyServiceBrowserDelegate {
+    func browser(_ browser: MCNearbyServiceBrowser, foundPeer peerID: MCPeerID, withDiscoveryInfo info: [String : String]?) {
+        browser.invitePeer(peerID, to: session, withContext: nil, timeout: 10)
+    }
+
+    func browser(_ browser: MCNearbyServiceBrowser, lostPeer peerID: MCPeerID) {}
+}
--- a/CoopRunning/SessionMessage.swift
+++ b/CoopRunning/SessionMessage.swift
@@ -0,0 +1,119 @@
+import Foundation
+
+struct SyncPlayPayload: Codable {
+    let trackID: String
+    let startUptime: TimeInterval
+    let startPosition: TimeInterval
+}
+
+struct TrackInfoPayload: Codable {
+    let trackID: String
+    let displayName: String
+}
+
+enum SessionMessage: Codable {
+    case hello
+    case libraryRequest
+    case trackInfo(TrackInfoPayload)
+    case trackRequest(String)
+    case play(SyncPlayPayload)
+    case pause
+    case seek(TimeInterval)
+    case syncRequest(TimeInterval)
+    case syncResponse(hostUptime: TimeInterval, peerUptime: TimeInterval)
+    case driftCorrection(position: TimeInterval, hostUptime: TimeInterval)
+
+    private enum CodingKeys: String, CodingKey {
+        case type
+        case payload
+        case position
+        case hostUptime
+        case peerUptime
+        case trackID
+        case displayName
+    }
+
+    private enum MessageType: String, Codable {
+        case hello
+        case libraryRequest
+        case trackInfo
+        case trackRequest
+        case play
+        case pause
+        case seek
+        case syncRequest
+        case syncResponse
+        case driftCorrection
+    }
+
+    init(from decoder: Decoder) throws {
+        let container = try decoder.container(keyedBy: CodingKeys.self)
+        let type = try container.decode(MessageType.self, forKey: .type)
+        switch type {
+        case .hello:
+            self = .hello
+        case .libraryRequest:
+            self = .libraryRequest
+        case .trackInfo:
+            let payload = try container.decode(TrackInfoPayload.self, forKey: .payload)
+            self = .trackInfo(payload)
+        case .trackRequest:
+            let trackID = try container.decode(String.self, forKey: .trackID)
+            self = .trackRequest(trackID)
+        case .play:
+            let payload = try container.decode(SyncPlayPayload.self, forKey: .payload)
+            self = .play(payload)
+        case .pause:
+            self = .pause
+        case .seek:
+            let position = try container.decode(TimeInterval.self, forKey: .position)
+            self = .seek(position)
+        case .syncRequest:
+            let hostUptime = try container.decode(TimeInterval.self, forKey: .hostUptime)
+            self = .syncRequest(hostUptime)
+        case .syncResponse:
+            let hostUptime = try container.decode(TimeInterval.self, forKey: .hostUptime)
+            let peerUptime = try container.decode(TimeInterval.self, forKey: .peerUptime)
+            self = .syncResponse(hostUptime: hostUptime, peerUptime: peerUptime)
+        case .driftCorrection:
+            let position = try container.decode(TimeInterval.self, forKey: .position)
+            let hostUptime = try container.decode(TimeInterval.self, forKey: .hostUptime)
+            self = .driftCorrection(position: position, hostUptime: hostUptime)
+        }
+    }
+
+    func encode(to encoder: Encoder) throws {
+        var container = encoder.container(keyedBy: CodingKeys.self)
+        switch self {
+        case .hello:
+            try container.encode(MessageType.hello, forKey: .type)
+        case .libraryRequest:
+            try container.encode(MessageType.libraryRequest, forKey: .type)
+        case .trackInfo(let payload):
+            try container.encode(MessageType.trackInfo, forKey: .type)
+            try container.encode(payload, forKey: .payload)
+        case .trackRequest(let trackID):
+            try container.encode(MessageType.trackRequest, forKey: .type)
+            try container.encode(trackID, forKey: .trackID)
+        case .play(let payload):
+            try container.encode(MessageType.play, forKey: .type)
+            try container.encode(payload, forKey: .payload)
+        case .pause:
+            try container.encode(MessageType.pause, forKey: .type)
+        case .seek(let position):
+            try container.encode(MessageType.seek, forKey: .type)
+            try container.encode(position, forKey: .position)
+        case .syncRequest(let hostUptime):
+            try container.encode(MessageType.syncRequest, forKey: .type)
+            try container.encode(hostUptime, forKey: .hostUptime)
+        case .syncResponse(let hostUptime, let peerUptime):
+            try container.encode(MessageType.syncResponse, forKey: .type)
+            try container.encode(hostUptime, forKey: .hostUptime)
+            try container.encode(peerUptime, forKey: .peerUptime)
+        case .driftCorrection(let position, let hostUptime):
+            try container.encode(MessageType.driftCorrection, forKey: .type)
+            try container.encode(position, forKey: .position)
+            try container.encode(hostUptime, forKey: .hostUptime)
+        }
+    }
+}
--- a/CoopRunning/SyncClock.swift
+++ b/CoopRunning/SyncClock.swift
@@ -0,0 +1,17 @@
+import Foundation
+
+enum SyncClock {
+    private static var hostOffset: TimeInterval = 0
+
+    static func uptime() -> TimeInterval {
+        ProcessInfo.processInfo.systemUptime
+    }
+
+    static func setHostOffset(hostUptime: TimeInterval, peerUptime: TimeInterval) {
+        hostOffset = hostUptime - peerUptime
+    }
+
+    static func convert(hostUptime: TimeInterval) -> TimeInterval {
+        hostUptime - hostOffset
+    }
+}
--- a/CoopRunningTests/CoopRunningTests.swift
+++ b/CoopRunningTests/CoopRunningTests.swift
@@ -0,0 +1,9 @@
+import XCTest
+@testable import CoopRunning
+
+final class CoopRunningTests: XCTestCase {
+    func testLibraryLoads() {
+        let library = LocalTrack.loadLibrary()
+        XCTAssertNotNil(library)
+    }
+}
--- a/README.md
+++ b/README.md
@@ -0,0 +1,20 @@
+# CoopRunning Sync (MVP)
+
+This is a minimal SwiftUI + MultipeerConnectivity prototype to sync **local MP3 playback** across iPhones. One device hosts and controls playback; peers join, receive the track file, and then sync playback.
+
+## Setup (Xcode)
+1. Create a new iOS App project in Xcode (SwiftUI, iOS 17+ or latest).
+2. Replace the generated Swift files with the files in `CoopRunning/`.
+3. Add these keys to your app's `Info.plist`:
+   - `NSLocalNetworkUsageDescription` = "Sync audio with nearby runners"
+   - `NSBonjourServices` (Array) with `_cooprun-sync._tcp`
+   - `NSBluetoothAlwaysUsageDescription` = "Find nearby runners"
+
+## How It Works
+- Host taps **Host**, peers tap **Join**.
+- Host imports an MP3 via **Import MP3**, then taps **Send Track** to push it to peers.
+- Host taps **Play** to broadcast a shared start time.
+- Host can tap **Sync Now** for a quick clock sync.
+
+## Notes
+- This is a prototype using `AVAudioEngine` host-time scheduling plus uptime-based sync. It is good enough for group runs, but not sample-accurate.
--- a/project.yml
+++ b/project.yml
@@ -0,0 +1,82 @@
+name: CoopRunning
+options:
+  bundleIdPrefix: de.felixfoertsch
+  deploymentTarget:
+    iOS: "26.0"
+settings:
+  base:
+    SWIFT_VERSION: 5.9
+    DEVELOPMENT_ASSET_PATHS: ""
+    TARGETED_DEVICE_FAMILY: "1" # iPhone
+    INFOPLIST_FILE: CoopRunning/Info.plist
+    CODE_SIGN_STYLE: Automatic
+    PRODUCT_BUNDLE_IDENTIFIER: de.felixfoertsch.cooprunning
+    DEVELOPMENT_TEAM: NG5W75WE8U
+    CODE_SIGN_IDENTITY: "Apple Development"
+    PROVISIONING_PROFILE_SPECIFIER: ""
+    ENABLE_USER_SCRIPT_SANDBOXING: "YES"
+    ASSETCATALOG_COMPILER_GENERATE_ASSET_SYMBOLS: "YES"
+    ASSETCATALOG_COMPILER_GENERATE_SWIFT_ASSET_SYMBOL_EXTENSIONS: "YES"
+    LOCALIZED_STRING_SWIFT_SYMBOLS: "YES"
+    SWIFT_STRING_CATALOGS: "YES"
+    STRING_CATALOG_GENERATE_SYMBOLS: "YES"
+    MARKETING_VERSION: 0.1.0
+    CURRENT_PROJECT_VERSION: 1
+    GENERATE_INFOPLIST_FILE: NO
+
+configs:
+  Debug: debug
+  Release: release
+
+schemes:
+  CoopRunning:
+    build:
+      targets:
+        CoopRunning: all
+    test:
+      targets:
+        - CoopRunningTests
+
+targets:
+  CoopRunning:
+    type: application
+    platform: iOS
+    sources:
+      - path: CoopRunning
+    resources:
+      - path: CoopRunning/LaunchScreen.storyboard
+    settings:
+      base:
+        PRODUCT_NAME: CoopRunning
+        ASSETCATALOG_COMPILER_APPICON_NAME: AppIcon
+        LOCALIZED_STRING_SWIFT_SYMBOLS: "YES"
+        SWIFT_STRING_CATALOGS: "YES"
+        STRING_CATALOG_GENERATE_SYMBOLS: "YES"
+    info:
+      path: CoopRunning/Info.plist
+      properties:
+        CFBundleDisplayName: CoopRunning
+        LSRequiresIPhoneOS: true
+        UILaunchStoryboardName: LaunchScreen
+        UISupportedInterfaceOrientations:
+          - UIInterfaceOrientationPortrait
+          - UIInterfaceOrientationPortraitUpsideDown
+          - UIInterfaceOrientationLandscapeLeft
+          - UIInterfaceOrientationLandscapeRight
+        NSLocalNetworkUsageDescription: "Sync audio with nearby runners"
+        NSBonjourServices:
+          - "_cooprun-sync._tcp"
+        NSBluetoothAlwaysUsageDescription: "Find nearby runners"
+
+  CoopRunningTests:
+    type: bundle.unit-test
+    platform: iOS
+    sources:
+      - path: CoopRunningTests
+    dependencies:
+      - target: CoopRunning
+    settings:
+      base:
+        LOCALIZED_STRING_SWIFT_SYMBOLS: "YES"
+        SWIFT_STRING_CATALOGS: "YES"
+        STRING_CATALOG_GENERATE_SYMBOLS: "YES"