如何从视频中提取图像？

Question

有人可以告诉我如何从视频中提取图像吗？ 我尝试了以下方法：

• 获取iPhone视频缩略图
• 在iPhone SDK中从视频网址或数据中获取缩略图
• 如何从iPhone SDK中的视频中提取截图？
• 使用AVFoundation从视频中读取UIimage（帧）, iPhone SDK > 3.0 . 视频缩略图？

等等。之后我做了这个：

源代码：

- (void)viewDidLoad
{
    videoPicker = [[UIImagePickerController alloc] init];
    [videoPicker setDelegate:self];
    videoPicker.sourceType =  UIImagePickerControllerSourceTypePhotoLibrary;
    NSArray *mediaTypesAllowed = [UIImagePickerController availableMediaTypesForSourceType:UIImagePickerControllerSourceTypePhotoLibrary];
    videoPicker.mediaTypes = mediaTypesAllowed;
    videoPicker.view.hidden = YES;
}


-(IBAction)imgPickerController
{
    [self presentModalViewController:videoPicker animated:YES];
    videoPicker.view.hidden = NO;
}

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
{
    // e.g.
    NSString *tempFilePath = [(NSURL *)[info valueForKey:UIImagePickerControllerMediaURL] absoluteString];

    NSLog(@"didFinishPickingMediaWithInfo: %@",tempFilePath);

    // e.g. /private/var/mobile/Applications/D1E784A4-EC1A-402B-81BF-F36D3A08A332/tmp/capture/capturedvideo.MOV
    tempFilePath = [tempFilePath substringFromIndex:16];

    NSLog(@"didFinishPickingMediaWithInfo: %@",tempFilePath);
    NSLog(@"===Try to save video to camera roll.===");
    NSLog(@"UIVideoAtPathIsCompatibleWithSavedPhotosAlbum: %@",UIVideoAtPathIsCompatibleWithSavedPhotosAlbum(tempFilePath)? @"YES":@"NO");

    // Check if the video file can be saved to camera roll.
    if (UIVideoAtPathIsCompatibleWithSavedPhotosAlbum(tempFilePath))
    {
        // YES. Copy it to the camera roll.
        UISaveVideoAtPathToSavedPhotosAlbum(tempFilePath, self, @selector(video:didFinishSavingWithError:contextInfo:),(__bridge_retained void *)tempFilePath );
    }

    [self dismissModalViewControllerAnimated:YES];
}

- (void)video:(NSString *)videoPath didFinishSavingWithError:(NSError *)error contextInfo:(NSString *)contextInfo
{
    NSLog(@"didFinishSavingWithError--videoPath in camera roll:%@",videoPath);
    NSLog(@"didFinishSavingWithError--videoPath in temp directory:%@",contextInfo);

    // The thumbnail jpg should located in this directory.
    NSString *thumbnailDirectory = [[contextInfo stringByDeletingLastPathComponent] stringByDeletingLastPathComponent];

    // Debug info. list all files in the directory of the video file.
    // e.g. /private/var/mobile/Applications/D1E784A4-EC1A-402B-81BF-F36D3A08A332/tmp/capture
    NSLog(@"%@",[contextInfo stringByDeletingLastPathComponent]);
    NSLog(@"%@",[[[NSFileManager defaultManager] contentsOfDirectoryAtPath:[contextInfo stringByDeletingLastPathComponent] error:nil] description]);

    // Debug info. list all files in the parent directory of the video file, i.e. the "~/tmp" directory.
    // e.g. /private/var/mobile/Applications/D1E784A4-EC1A-402B-81BF-F36D3A08A332/tmp
    NSLog(@"%@",thumbnailDirectory);
    NSLog(@"%@",[[[NSFileManager defaultManager] contentsOfDirectoryAtPath:thumbnailDirectory error:nil] description]);
    ///////////////////

    // Find the thumbnail for the video just recorded.
    NSString *file,*latestFile;

    NSDate *latestDate = [NSDate distantPast];
    NSDirectoryEnumerator *dirEnum = [[NSFileManager defaultManager] enumeratorAtPath:[[contextInfo stringByDeletingLastPathComponent]stringByDeletingLastPathComponent]];

    // Enumerate all files in the ~/tmp directory
    while (file = [dirEnum nextObject])
    {
        // Only check files with jpg extension.
        if ([[file pathExtension] isEqualToString: @"jpg"]) 
        {
            NSLog(@"***latestDate:%@",latestDate);
            NSLog(@"***file name:%@",file);
            NSLog(@"***NSFileSize:%@", [[dirEnum fileAttributes] valueForKey:@"NSFileSize"]);
            NSLog(@"***NSFileModificationDate:%@", [[dirEnum fileAttributes] valueForKey:@"NSFileModificationDate"]);

            // Check if current jpg file is the latest one.
            if ([(NSDate *)[[dirEnum fileAttributes] valueForKey:@"NSFileModificationDate"] compare:latestDate] == NSOrderedDescending)
            {
                latestDate = [[dirEnum fileAttributes] valueForKey:@"NSFileModificationDate"];
                latestFile = file;
                NSLog(@"***latestFile changed:%@",latestFile);
            }
        }
    }

    // The thumbnail path.
    latestFile = [NSTemporaryDirectory() stringByAppendingPathComponent:latestFile];
    NSLog(@"****** The thumbnail file should be this one:%@",latestFile);

    UIImage *img = [[UIImage alloc] initWithContentsOfFile:latestFile];
    UIImageView *imgView = [[UIImageView alloc] initWithFrame:CGRectMake(150, 150, 100, 100)];
    [imgView setImage:img];
    imgView.layer.borderWidth = 2.0;
    [self.view addSubview:imgView];

    // Your code ...
    // Your code ...
    // Your code ...
}

尽管我已经做了所有的事情，但还是没有达到我想要达到的地方，我仍然没有得到图片。现在我被卡住了，请有人帮帮我！谢谢 :)

- Nikhil Bansal

Answer 1

从电影中提取缩略图的简单方法是使用MPMoviePlayerController类及其- thumbnailImageAtTime:timeOption:方法。

例如，你有一个文件路径url：

NSURL *tempFilePathURL = ...;
MPMoviePlayerController *player = [[MPMoviePlayerController alloc] initWithContentURL: tempFilePathURL];
UIImage *thumbnail = [player thumbnailImageAtTime:THUMBNAIL_TIME timeOption:MPMovieTimeOptionExact];
[player release];

我在我的代码中使用它，它起作用了。

- Eldar Markov

---

请问如何获取这个缩略图的路径和扩展名？ - Nikhil Bansal

根据我的示例，您将获得UIImage对象。然后，您可以将其保存为png或jpg格式。 - Eldar Markov

Answer 2

thumbnailImageAtTime:timeOption自iOS 7.0起已被弃用。这里提供一种替代方法：

+ (UIImage *)extractFirstFrameFromFilepath:(NSString *)filepath
{
    AVURLAsset *movieAsset = [[AVURLAsset alloc] initWithURL:[NSURL fileURLWithPath:filepath] options:nil];
    AVAssetImageGenerator *assetImageGemerator = [[AVAssetImageGenerator alloc] initWithAsset:movieAsset];
    assetImageGemerator.appliesPreferredTrackTransform = YES;
    CGImageRef frameRef = [assetImageGemerator copyCGImageAtTime:CMTimeMake(1, 2) actualTime:nil error:nil];
    return [[UIImage alloc] initWithCGImage:frameRef];
}

- zvjerka24

---

我们能否重写代码，使其遍历整个视频？或者每隔1秒钟执行一次。 - user2849654

Answer 3

Swift 版本

    func getThumbOfVideo(fileURL: URL) -> UIImage? {
        let movieAsset = AVURLAsset(url: fileURL)
        let assetImageGenerator = AVAssetImageGenerator(asset: movieAsset)
        assetImageGenerator.appliesPreferredTrackTransform = true

        var thumbnail: UIImage?
        do {
            let cgImage = try assetImageGenerator.copyCGImage(at: CMTimeMake(value: 0, timescale: 1000), actualTime: nil)
            thumbnail = UIImage(cgImage: cgImage)
        } catch {
            print(error)
        }

        return thumbnail
    }

如果您需要在整个视频中使用缩略图数组，则可以使用AVAssetImageGenerator类的以下API

func generateCGImagesAsynchronously(forTimes requestedTimes: [NSValue], 
                  completionHandler handler: @escaping AVAssetImageGeneratorCompletionHandler)

设置所需缩略图图像分辨率的属性如下

assetImageGenerator.maximumSize

- Learner