Extract frame from video in swift

Question

I'm trying to extract frames as UIImages from a video in Swift. I found several Objective C solutions but I'm having trouble finding anything in Swift. Assuming the following is correct can someone either help me to convert the following to Swift or give me their own take on how to do this?

Source: Grabbing the first frame of a video from UIImagePickerController?

- (UIImage *)imageFromVideo:(NSURL *)videoURL atTime:(NSTimeInterval)time {
    
    AVURLAsset *asset = [[AVURLAsset alloc] initWithURL:videoURL options:nil];
    NSParameterAssert(asset);
    AVAssetImageGenerator *assetIG =
    [[AVAssetImageGenerator alloc] initWithAsset:asset];
    assetIG.appliesPreferredTrackTransform = YES;
    assetIG.apertureMode = AVAssetImageGeneratorApertureModeEncodedPixels;
    
    CGImageRef thumbnailImageRef = NULL;
    CFTimeInterval thumbnailImageTime = time;
    NSError *igError = nil;
    thumbnailImageRef =
    [assetIG copyCGImageAtTime:CMTimeMake(thumbnailImageTime, 60)
                    actualTime:NULL
                         error:&igError];
    
    if (!thumbnailImageRef)
        NSLog(@"thumbnailImageGenerationError %@", igError );
    
    UIImage *image = thumbnailImageRef
    ? [[UIImage alloc] initWithCGImage:thumbnailImageRef]
    : nil;
    
    return image;
}

Answer 1

It actually did work.

func imageFromVideo(url: URL, at time: TimeInterval) -> UIImage? {
    let asset = AVURLAsset(url: url)

    let assetIG = AVAssetImageGenerator(asset: asset)
    assetIG.appliesPreferredTrackTransform = true
    assetIG.apertureMode = AVAssetImageGeneratorApertureModeEncodedPixels

    let cmTime = CMTime(seconds: time, preferredTimescale: 60)
    let thumbnailImageRef: CGImage
    do {
        thumbnailImageRef = try assetIG.copyCGImage(at: cmTime, actualTime: nil)
    } catch let error {
        print("Error: \(error)")
        return nil
    }

    return UIImage(cgImage: thumbnailImageRef)
}

But remember that this function is synchronous and it's better not to call it on the main queue.

You can do either this:

DispatchQueue.global(qos: .background).async {
    let image = self.imageFromVideo(url: url, at: 0)

    DispatchQueue.main.async {
        self.imageView.image = image
    }
}

Or use generateCGImagesAsynchronously instead of copyCGImage.

Answer 2

Here's a SWIFT 5 alternative to Dmitry's solution, to not have to worry about what queue you're on:

public func imageFromVideo(url: URL, at time: TimeInterval, completion: @escaping (UIImage?) -> Void) {
    DispatchQueue.global(qos: .background).async {
        let asset = AVURLAsset(url: url)

        let assetIG = AVAssetImageGenerator(asset: asset)
        assetIG.appliesPreferredTrackTransform = true
        assetIG.apertureMode = AVAssetImageGenerator.ApertureMode.encodedPixels

        let cmTime = CMTime(seconds: time, preferredTimescale: 60)
        let thumbnailImageRef: CGImage
        do {
            thumbnailImageRef = try assetIG.copyCGImage(at: cmTime, actualTime: nil)
        } catch let error {
            print("Error: \(error)")
            return completion(nil)
        }

        DispatchQueue.main.async {
            completion(UIImage(cgImage: thumbnailImageRef))
        }
    }
}

Here's now to use it:

imageFromVideo(url: videoUrl, at: 0) { image in
   // Do something with the image here
}