在 Swift (iOS) 中从视频创建帧

Question

有一个持续时间为 3 秒的视频文件。我需要创建 30 帧 - UIImages。每 0.1 秒捕获一次图像。 我尝试使用 AVAssetImageGenerator 和 CMTimeMake，但我总是得到 30 个相似的图像，或者 15 个相似的图像和 15 个相似的图像。

请帮助了解如何从该视频中制作这种幻灯片。或者也许有更好的方法来做到这一点。

请看下面的代码：

static func generate_Thumbnails(forVideoWithURL url : URL) -> [UIImage]? {
    let asset = AVAsset(url: url)
    var result: [UIImage] = []
    let assetImgGenerator = AVAssetImageGenerator(asset: asset)
    assetImgGenerator.appliesPreferredTrackTransform = true
    for i in 1...30 {
        let time: CMTime = CMTimeMake(value: Int64(i), timescale: 10)
        do {
            let img: CGImage = try assetImgGenerator.copyCGImage(at: time, actualTime: nil)
            let frameImg: UIImage = UIImage(cgImage: img)
            result.append(frameImg)
        } catch {
            //return nil
        }
    }
    return result
}

Answer 1

我还没有阅读 AVAssetImageGenerator 的文档，但实际上我每秒只能生成 1 张图像。因此，您应该能够在 1、2 和 3 秒（但不是 30 秒）时获得图像。这是我用来生成图像的代码，和你的很相似。

private func getPreviewImage(forURL url: URL, atSeconds seconds: Double) -> UIImage? {
        let asset = AVURLAsset(url: url)
        let generator = AVAssetImageGenerator(asset: asset)
        generator.appliesPreferredTrackTransform = true

        let timestamp = CMTime(seconds: seconds, preferredTimescale: 100)

        do {
            let imageRef = try generator.copyCGImage(at: timestamp, actualTime: nil)
            return UIImage(cgImage: imageRef)
        }
        catch let error as NSError
        {
            print("Image generation failed with error \(error)")
            return nil
        }
    }

Answer 2

我尝试了Amin Benarieb 的解决方案，它似乎有效：

static func toImages(fromVideoUrl url: URL) -> [UIImage]? {
    let asset = AVAsset(url: url)
    guard let reader = try? AVAssetReader(asset: asset) else { return nil }
    let videoTrack = asset.tracks(withMediaType: .video).first!
    let outputSettings = [String(kCVPixelBufferPixelFormatTypeKey): NSNumber(value: kCVPixelFormatType_32BGRA)]
    let trackReaderOutput = AVAssetReaderTrackOutput(track: videoTrack, outputSettings: outputSettings)
    reader.add(trackReaderOutput)
    reader.startReading()
    var images = [UIImage]()
    while reader.status == .reading {
        autoreleasepool {
            if let sampleBuffer = trackReaderOutput.copyNextSampleBuffer() {
                if let imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer) {
                    let ciImage = CIImage(cvImageBuffer: imageBuffer)
                    images.append(UIImage(ciImage: ciImage))
                }
            }
        }
    }
    return images
}