我正在尝试获取所选视频的缩略图。它似乎确实创建了缩略图，但在将其上传到firebase时崩溃了我相信它会在thumbnailStorageRef处崩溃。相关代码如下:guardletimagePickerUrl=info[UIImagePickerControllerMediaURL]as?URLelse{return}letvideoUrl=imagePickerUrl//Generateimagethumbnail.letasset:AVAsset=AVAsset(url:videoUrlasURL)letimageGenerator=AVAssetImageGenerator(a