无法从图库中的视频生成缩略图

Question

我正在向用户显示一个图像选择器以从图库中选择一个视频。那行得通，我通过了媒体类型 ["public.movi​​e"] 并且画廊的所有视频都显示出来以供拾取。当用户选择它时，我会在我的代表中收到：

extension VNInventoryCollectionVC: UIImagePickerControllerDelegate {
    func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [UIImagePickerController.InfoKey: Any]) {
        let info = convertFromUIImagePickerControllerInfoKeyDictionary(info)
        if let pickedImage = info[convertFromUIImagePickerControllerInfoKey(UIImagePickerController.InfoKey.originalImage)] as? UIImage
        {
            pickImageCallback?(pickedImage)
        }
        if let videoURL = info["UIImagePickerControllerReferenceURL"] as? URL
        {
            print(videoURL)
            pickImageCallback?(videoURL)
        }
        dismiss(animated: true)
       
    }
}

回调后，我尝试从该视频创建图像缩略图，但这是我无法做到的：

let thumbnail = getThumbnailFrom(path: multimedia.video!)
cell.image.image = thumbnail

生成缩略图的函数是：

func getThumbnailFrom(path: URL) -> UIImage? {
    do {
        print("Video URL: \(path)")
        print("Video absolute URL: \(path.absoluteURL)")
        //let asset = AVURLAsset(url: path.absoluteURL! , options: nil)
        var asset : AVAsset = AVAsset(url: path.absoluteURL) as! AVAsset
        let imgGenerator = AVAssetImageGenerator(asset: asset)
        imgGenerator.appliesPreferredTrackTransform = true
        let cgImage = try imgGenerator.copyCGImage(at: CMTimeMake(value: 0, timescale: 1), actualTime: nil)
        let thumbnail = UIImage(cgImage: cgImage)

        return thumbnail

    } catch let error {
        print("*** Error generating thumbnail: \(error.localizedDescription)")
        return nil
    }
}

在控制台中显示的视频网址是：

Video URL: assets-library://asset/asset.MP4?id=84D1CEDD-7AE4-4FE5-897E-47608DC2CFF0&ext=MP4
Video absolute URL: assets-library://asset/asset.MP4?id=84D1CEDD-7AE4-4FE5-897E-47608DC2CFF0&ext=MP4

显示的错误是无法打开文件。中断的行是：

let cgImage = try imgGenerator.copyCGImage(at: CMTimeMake(value: 0, timescale: 1), actualTime: nil)

我想问题出在 url，我有一个资产 url，我需要一个绝对文件路径或类似的东西。

Answer 1

使用UIImagePickerController.InfoKey.mediaURL 键入信息字典。 UIImagePickerController.InfoKey.referenceURL 是 deprecated。

func didSelectVideo(at url: URL) {
    let asset = AVAsset(url: url)
    let generator = AVAssetImageGenerator(asset: asset)
    generator.appliesPreferredTrackTransform = true
    let cgImage = try! generator.copyCGImage(at: CMTimeMake(value: 0, timescale: 1), actualTime: nil)
    let thumbnail = UIImage(cgImage: cgImage)
    cell.image.image = thumbnail
}

func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [UIImagePickerController.InfoKey : Any]) {
    dismiss(animated: true) {
        guard let url = info[.mediaURL] as? URL else { return }
        self.didSelectVideo(at: url)
    }
}