iOS - How to get thumbnail from video without play?

Question

I'm trying to get thumbnail from video and show it in my tableview. Here is my code:

- (UIImage *)imageFromVideoURL:(NSURL *)contentURL {
    AVAsset *asset = [AVAsset assetWithURL:contentURL];

    //  Get thumbnail at the very start of the video
    CMTime thumbnailTime = [asset duration];
    thumbnailTime.value = 25;

    //  Get image from the video at the given time
    AVAssetImageGenerator *imageGenerator = [[AVAssetImageGenerator alloc] initWithAsset:asset];

    CGImageRef imageRef = [imageGenerator copyCGImageAtTime:thumbnailTime actualTime:NULL error:NULL];
    UIImage *thumbnail = [UIImage imageWithCGImage:imageRef];
    CGImageRelease(imageRef);

    return thumbnail;
}

But image allways return black. What's wrong?

Answer 1

Using Swift 5, as an extension function on AVAsset:

import AVKit

extension AVAsset {

    func generateThumbnail(completion: @escaping (UIImage?) -> Void) {
        DispatchQueue.global().async {
            let imageGenerator = AVAssetImageGenerator(asset: self)
            let time = CMTime(seconds: 0.0, preferredTimescale: 600)
            let times = [NSValue(time: time)]
            imageGenerator.generateCGImagesAsynchronously(forTimes: times, completionHandler: { _, image, _, _, _ in
                if let image = image {
                    completion(UIImage(cgImage: image))
                } else {
                    completion(nil)
                }
            })
        }
    }
}

Usage:

            AVAsset(url: url).generateThumbnail { [weak self] (image) in
                DispatchQueue.main.async {
                    guard let image = image else { return }
                    self?.imageView.image = image
                }
            }