在swift中从视频中提取帧

Question

我正试图从Swift中的视频中提取帧作为UIImages.我找到了几个Objective C解决方案,但我在Swift中找不到任何东西.假设以下是正确的,有人可以帮助我将以下内容转换为Swift或者让我自己采取如何做到这一点？

- (UIImage *)imageFromVideo:(NSURL *)videoURL atTime:(NSTimeInterval)time {

    // courtesy of memmons
    // http://stackoverflow.com/questions/1518668/grabbing-the-first-frame-of-a-video-from-uiimagepickercontroller

    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

它确实起了作用.

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)
}

但请记住,此函数是同步的,最好不要在主队列上调用它.

你可以这样做:

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

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

或者用generateCGImagesAsynchronously而不是copyCGImage.

Answer 2

这是Dmitry 解决方案的SWIFT 5替代方案，无需担心您所在的队列：

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))
        }
    }
}

现在就来使用它：

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