如何在PhotosPicker中用户选视频后立即检测时长以限制上传？

iOS 14+ 原生推荐方案 #

借助PHPicker的NSItemProvider，可以直接在内存中加载选中的视频为AVAsset，无需写入本地存储就能获取时长：

实现代码 #

1. 初始化并展示选择器：

let config = PHPickerConfiguration(photoLibrary: PHPhotoLibrary.shared())
config.filter = .videos
config.selectionLimit = 1
let picker = PHPickerViewController(configuration: config)
picker.delegate = self
present(picker, animated: true)

2. 处理选中结果：

func picker(_ picker: PHPickerViewController, didFinishPicking results: [PHPickerResult]) {
    picker.dismiss(animated: true)
    
    guard let result = results.first else { return }
    guard result.itemProvider.canLoadObject(ofClass: AVAsset.self) else {
        // 处理不支持的资源类型
        return
    }
    
    result.itemProvider.loadObject(ofClass: AVAsset.self) { [weak self] asset, error in
        guard let videoAsset = asset as? AVAsset, error == nil else {
            // 处理加载失败
            return
        }
        
        let duration = CMTimeGetSeconds(videoAsset.duration)
        DispatchQueue.main.async {
            if duration > 20 {
                // 触发超时时长操作，例如下发提示
                let alert = UIAlertController(title: "提示", message: "视频时长不得超过20秒", preferredStyle: .alert)
                alert.addAction(UIAlertAction(title: "确定", style: .default))
                self?.present(alert, animated: true)
            } else {
                // 处理合规视频
            }
        }
    }
}

关键优势 #

• 无需将视频写入本地存储，内存中直接处理，性能更优
• 无需申请照片库读写权限，仅依赖用户主动选择，符合iOS隐私要求
• 支持批量选择检测（调整selectionLimit即可）

iOS 13及以下兼容方案 #

如果需要适配旧版本系统，可使用UIImagePickerController配合PHAsset实现：

实现代码 #

1. 初始化选择器：

let picker = UIImagePickerController()
picker.sourceType = .photoLibrary
picker.mediaTypes = ["public.movie"]
picker.delegate = self
present(picker, animated: true)

2. 获取视频时长：

func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [UIImagePickerController.InfoKey : Any]) {
    picker.dismiss(animated: true)
    
    guard let assetURL = info[.mediaURL] as? URL else { return }
    let fetchResult = PHAsset.fetchAssets(withALAssetURLs: [assetURL], options: nil)
    
    guard let asset = fetchResult.firstObject else { return }
    let duration = asset.duration
    if duration > 20 {
        // 触发超时时长操作
    }
}

注意事项 #

• 需要在Info.plist中添加NSPhotoLibraryUsageDescription申请照片库读取权限
• 依赖PHAsset的获取，需确保用户已授予对应权限

内容的提问来源于stack exchange，提问作者Swink