Swift Thumbnail on the fly

Description

It is quite painful where you have a decent video API, but doesn’t provide you with a thumbnail. This makes it very hard to demonstrate to users what the video looks like a first glance.

Therefore, we have came up with a technique that buffers the first minute of a video and generate a thumbnail on the fly.

Code

Using AVAsset, we can write an extension that dispatches a thread dedicated to generate a thumbnail (also duration of the video in the case below).

extension AVAsset {
    func generateThumbnail(completion: @escaping (UIImage?, Int?) -> Void) {
        DispatchQueue.global().async {
            let imageGenerator = AVAssetImageGenerator(asset: self)
            let time = CMTime(seconds: 60.0, preferredTimescale: 600)
            let times = [NSValue(time: time)]
            let duration = Int(self.duration.seconds)
            imageGenerator.generateCGImagesAsynchronously(forTimes: times, completionHandler: { _, image, _, _, _ in
                if let image = image {
                    completion(UIImage(cgImage: image), duration)
                } else {
                    completion(nil, nil)
                }
            })
        }
    }
}

More

For more information, checkout

• AVAsset - AVFoundation | Apple Developer Documentation
• Generate images from AVAsset with AVAssetImageGenerator