Generated Subtitles & Subtitle Style Preview

import SwiftUI
import AVFoundation
import AVKit

struct SubtitleStylePreviewDemo: View {
    private let player: AVPlayer
    private let playerLayer: AVPlayerLayer

    @State private var styleProfiles: [AVCaptionStyleProfile] = []
    @State private var selectedProfile: AVCaptionStyleProfile?
    @State private var isPreviewing = false

    init() {
        let url = URL(string: "https://devstreaming-cdn.apple.com/videos/wwdc/2023/101/4/5BFC93F8-C8D2-4A74-B7C5-8C1E8CF77345/cmaf/hvc/2160p_16800/prog_index.m3u8")!
        let item = AVPlayerItem(url: url)
        let p = AVPlayer(playerItem: item)
        player = p
        playerLayer = AVPlayerLayer(player: p)
    }

    var body: some View {
        VStack(spacing: 16) {
            PlayerLayerView(playerLayer: playerLayer)
                .frame(height: 220)
                .cornerRadius(12)
                .onAppear {
                    loadStyleProfiles()
                    player.play()
                }
                .onDisappear {
                    player.pause()
                    if isPreviewing {
                        stopPreview()
                    }
                }

            Text("Subtitle Styles").font(.headline)

            ScrollView(.horizontal, showsIndicators: false) {
                HStack(spacing: 12) {
                    ForEach(styleProfiles, id: \.profileID) { profile in
                        Button(action: {
                            previewStyle(profile)
                        }) {
                            Text(profile.localizedName)
                                .padding(.horizontal, 14)
                                .padding(.vertical, 8)
                                .background(
                                    selectedProfile?.profileID == profile.profileID
                                        ? Color.accentColor : Color(.systemGray5)
                                )
                                .foregroundColor(
                                    selectedProfile?.profileID == profile.profileID
                                        ? .white : .primary
                                )
                                .cornerRadius(8)
                        }
                    }
                }
                .padding(.horizontal)
            }

            HStack(spacing: 16) {
                Button("Stop Preview") {
                    stopPreview()
                }
                .disabled(!isPreviewing)

                Button("Apply Style") {
                    applySelectedStyle()
                }
                .disabled(selectedProfile == nil)
                .buttonStyle(.borderedProminent)
            }
        }
        .padding()
    }

    private func loadStyleProfiles() {
        styleProfiles = AVCaptionStyleProfile.availableProfiles()
    }

    private func previewStyle(_ profile: AVCaptionStyleProfile) {
        selectedProfile = profile
        isPreviewing = true
        // Pass nil for text to show localized system placeholder text.
        // Use position offset to avoid overlapping custom controls at the bottom.
        playerLayer.showSubtitleStylePreview(
            forProfileID: profile.profileID,
            text: nil,
            position: CGPoint(x: 0, y: -40)
        )
    }

    private func stopPreview() {
        isPreviewing = false
        playerLayer.stopSubtitleStylePreview()
    }

    private func applySelectedStyle() {
        guard let profile = selectedProfile else { return }
        stopPreview()
        AVCaptionStyleProfile.setCurrentProfile(profile)
    }
}

// UIViewRepresentable wrapper to host AVPlayerLayer
struct PlayerLayerView: UIViewRepresentable {
    let playerLayer: AVPlayerLayer

    func makeUIView(context: Context) -> UIView {
        let view = UIView()
        view.backgroundColor = .black
        playerLayer.videoGravity = .resizeAspect
        view.layer.addSublayer(playerLayer)
        return view
    }

    func updateUIView(_ uiView: UIView, context: Context) {
        playerLayer.frame = uiView.bounds
    }
}