stream - 无法在collectionView Swift 4中使用来自实时流（m3u8）的图像缩略图

Question

这是我的代码（用 Swift 4，xcode 9.2 编写）的一部分，我想在其中执行此操作。

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "customCell", for: indexPath) as! CustomCollectionViewCell
if let thumbnailImage = getThumbnailImage(forUrl: str!) {
        cell.imageView.image = thumbnailImage
    }
    cell.nameLabel.text = devices[indexPath.row].name.capitalized
    print(devices[indexPath.row].url)
    return cell
}

和 getThumnailImage 函数

func getThumbnailImage(forUrl url: URL) -> UIImage? {
    let asset: AVAsset = AVAsset(url: url)
    let imageGenerator = AVAssetImageGenerator(asset: asset)
    do {
        let thumbnailImage = try imageGenerator.copyCGImage(at: CMTimeMake(1, 60) , actualTime: nil)
        return UIImage(cgImage: thumbnailImage)
    } catch let error {
        print(error)
    }
    return nil
}

当我运行它时，我得到这个错误：

Error Domain=AVFoundationErrorDomain Code=-11850 "Operation Stopped" UserInfo={NSLocalizedFailureReason=服务器配置不正确。, NSLocalizedDescription=Operation Stopped, NSUnderlyingError=0x61c00044fbd0 {Error Domain=NSOSStatusErrorDomain Code=-12939 "(null)"}}