从库中提取的视频的 UIImagePickerController 缩略图

Posted 2023-03-29

【中文标题】从库中提取的视频的 UIImagePickerController 缩略图

【英文标题】：UIImagePickerController thumbnail of video which is pick up from library

【发布时间】：2011-08-08 19:33:16

【问题描述】：

我正在尝试使用 UIImagePickerController 从库中获取视频的缩略图。

这是我的代码。如果我使用相机录制视频，我可以获得视频的缩略图。但是，如果我从图书馆拿起视频，我就无法获得缩略图。有人知道为什么吗？

-(void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info

    NSString *mediaType = [info objectForKey:UIImagePickerControllerMediaType];

    if ([mediaType isEqualToString:(NSString *)kUTTypeMovie])
    
        NSURL *mediaUrl = [info objectForKey:UIImagePickerControllerMediaURL];

        MPMoviePlayerController *moviePlayer = [[MPMoviePlayerController alloc] initWithContentURL:mediaUrl];
        moviePlayer.shouldAutoplay = NO;
        UIImage *thumbnail = [[moviePlayer thumbnailImageAtTime:0.0 timeOption:MPMovieTimeOptionNearestKeyFrame] retain];
        [imageView setImage:thumbnail];  //imageView is a UIImageView

        [moviePlayer release];
        [thumbnail release];
        [self dismissModalViewControllerAnimated:YES];
    

【参考方案1】：

我遇到了一个半相关的问题，最终放弃了使用 MPMoviePlayer 生成缩略图。尝试改用AVAssetImageGenerator。 Apple 讨论使用 AVAssetImageGenerator 创建缩略图here。这是我自己的示例代码，它抓取一个缩略图。您将需要包含 AVFoundation 框架。

AVURLAsset *asset = [[AVURLAsset alloc] initWithURL:vidPath options:nil];
AVAssetImageGenerator *gen = [[AVAssetImageGenerator alloc] initWithAsset:asset];
gen.appliesPreferredTrackTransform = YES;
CMTime time = CMTimeMakeWithSeconds(0.0, 600);
NSError *error = nil;
CMTime actualTime;

CGImageRef image = [gen copyCGImageAtTime:time actualTime:&actualTime error:&error];
UIImage *thumb = [[UIImage alloc] initWithCGImage:image];
CGImageRelease(image);
[gen release];

【参考方案2】：

AssetsLibrary 框架具有您所需要的 ALAssetsLibrary 和 ALAsset 类。此代码适用于照片和视频，缩略图与您在选择器中看到的完全相同。

- (void) imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info

    [[ALAssetsLibrary new] assetForURL:info[UIImagePickerControllerReferenceURL] resultBlock:^(ALAsset *asset) 
        imageView.image = [UIImage imageWithCGImage:asset.thumbnail];
     failureBlock:^(NSError *error) 
        // handle error
    ];
    [self dismissViewControllerAnimated:YES completion:nil];

请注意，ios 8 上的 Photo Stream 相册存在一个错误，请参阅ALAssetsLibrary assetForURL: always returning nil for photos in “My Photo Stream” in iOS 8.1 了解解决方法。

【讨论】：

在 iOS 8 及更高版本上，Apple 建议使用 Photos framework 而不是 ALAssetsLibrary。这将是比回退到enumerateGroupsWithTypes:usingBlock: 更好的方法。

我认为该评论属于链接问题。

【参考方案3】：

func videoSnapshot(filePathLocal:URL) -> UIImage? 
    do
    
        let asset = AVURLAsset(url: filePathLocal)
        let imgGenerator = AVAssetImageGenerator(asset: asset)
        imgGenerator.appliesPreferredTrackTransform = true
        let cgImage = try imgGenerator.copyCGImage(at:CMTimeMake(Int64(0), Int32(1)),actualTime: nil)
        let thumbnail = UIImage(cgImage: cgImage)
        return thumbnail
    
    catch let error as NSError
    
        print("Error generating thumbnail: \(error)")
        return nil
    

【讨论】：

解决问题

【参考方案4】：

Swift 5及以上

func thumbnailForVideo(url: URL) -> UIImage? 
    let asset = AVAsset(url: url)
    let assetImageGenerator = AVAssetImageGenerator(asset: asset)
    assetImageGenerator.appliesPreferredTrackTransform = true

    var time = asset.duration
    time.value = min(time.value, 2)

    do 
        let imageRef = try assetImageGenerator.copyCGImage(at: time, actualTime: nil)
        return UIImage(cgImage: imageRef)
     catch 
        print("failed to create thumbnail")
        return nil
    

【参考方案5】：

斯威夫特 3.1

我已经创建了一个类函数并在参数中传递了你的 url

class func captureThumbnail(withVideoURL videoURL:URL,secs:Int,preferredTimeScale scale:Int,completionHandler:((UIImage?) ->Void)?) -> Void

    //let seconds : Int64 = 10
    // let preferredTimeScale : Int32 = 1

    DispatchQueue.global().async 

        do
        
            let asset = AVURLAsset(url: videoURL)

            let imgGenerator = AVAssetImageGenerator(asset: asset)
            imgGenerator.appliesPreferredTrackTransform = true
            let cgImage = try imgGenerator.copyCGImage(at:CMTimeMake(Int64(secs), Int32(scale)),actualTime: nil)
            let thumbnail = UIImage(cgImage: cgImage)
            completionHandler?(thumbnail)
        
        catch let error as NSError
        
            print("Error generating thumbnail: \(error)")
            completionHandler?(nil)