向视频添加水印非常慢

Question

我正在使用 AVComposition 为视频呈现水印。这个过程大约需要 15 秒，这对于 20 秒的视频来说似乎不太合适。 我的导出设置是：

let exporter = AVAssetExportSession.init(asset: mixComposition, presetName: AVAssetExportPresetHighestQuality)
    exporter?.outputURL = outputPath
    exporter?.outputFileType = AVFileType.mp4
    exporter?.shouldOptimizeForNetworkUse = true
    exporter?.videoComposition = mainCompositionInst
    DispatchQueue.main.async {
        exporter?.exportAsynchronously(completionHandler: {

            if exporter?.status == AVAssetExportSessionStatus.completed {
                completion(true, exporter)
            }else{
                completion(false, exporter)
            }

        })
    }

这是我添加水印的方式：

    //Creating image layer
    let overlayLayer = CALayer()
    let overlayImage: UIImage = image
    overlayLayer.contents = overlayImage.cgImage
    overlayLayer.frame = CGRect(x: 0, y: 0, width: size.width, height: size.height)
    overlayLayer.contentsGravity = kCAGravityResizeAspectFill
    overlayLayer.masksToBounds = true

    //Creating parent and video layer
    let parentLayer = CALayer()
    let videoLayer = CALayer()
    parentLayer.frame = CGRect(x: 0, y: 0, width: size.width, height: size.height)
    videoLayer.frame = CGRect(x: 0, y: 0, width: size.width, height: size.height)
    parentLayer.addSublayer(videoLayer)
    parentLayer.addSublayer(overlayLayer)

    //Adding those layers to video
    composition.animationTool = AVVideoCompositionCoreAnimationTool(postProcessingAsVideoLayer: videoLayer, in: parentLayer)
}

这就是我最终转换视频的方式：

 let videoLayerInstruction = AVMutableVideoCompositionLayerInstruction.init(assetTrack: videoTrack!)
    let videoAssetTrack = videoAsset.tracks(withMediaType: AVMediaType.video)[0]
    var videoAssetOrientation = UIImageOrientation.up
    var isVideoAssetPortrait = false
    let videoTransform = videoAssetTrack.preferredTransform

    if videoTransform.a == 0 && videoTransform.b == 1.0 && videoTransform.c == -1.0 && videoTransform.d == 0 {
        videoAssetOrientation = .right
        isVideoAssetPortrait = true
    }
    if videoTransform.a == 0 && videoTransform.b == -1.0 && videoTransform.c == 1.0 && videoTransform.d == 0 {
        videoAssetOrientation = .left
        isVideoAssetPortrait = true
    }
    if videoTransform.a == 1.0 && videoTransform.b == 0 && videoTransform.c == 0 && videoTransform.d == 1.0 {
        videoAssetOrientation = .up
    }
    if videoTransform.a == -1.0 && videoTransform.b == 0 && videoTransform.c == 0 && videoTransform.d == -1.0 {
        videoAssetOrientation = .down
    }

    videoLayerInstruction.setTransform(videoAssetTrack.preferredTransform, at: kCMTimeZero)

    //Add instructions
    mainInstruction.layerInstructions = [videoLayerInstruction]
    let mainCompositionInst = AVMutableVideoComposition()
    let naturalSize : CGSize!
    if isVideoAssetPortrait {
        naturalSize = CGSize(width: videoAssetTrack.naturalSize.height, height: videoAssetTrack.naturalSize.width)
    } else {
        naturalSize = videoAssetTrack.naturalSize
    }

所以我现在的问题是，如何提高将水印合并到视频的性能？对于任何类型的最终用户来说，15 秒是完全不可接受的。此外，我需要通过 Internet 传输此视频，因此加载屏幕显示其美丽的时间将超过总共大约 20 秒。

Answer 1

根据Apple Documentation，尝试使用类AVAsynchronousCIImageFilteringRequest

概述

在使用 init(asset:applyingCIFiltersWithHandler:) 方法为 Core Image 过滤创建合成时使用此类。在该方法调用中，您提供一个块以供 AVFoundation 在处理每一帧视频时调用，该块的唯一参数是 AVAsynchronousCIImageFilteringRequest 对象。将该对象用于要过滤的视频帧图像，并允许您将过滤后的图像返回到 AVFoundation 以进行显示或导出。清单 1 显示了将过滤器应用于资产的示例。

    let filter = CIFilter(name: "CIGaussianBlur")!
    let composition = AVVideoComposition(asset: asset, applyingCIFiltersWithHandler: { request in

    // Clamp to avoid blurring transparent pixels at the image edges
    let source = request.sourceImage.imageByClampingToExtent()
    filter.setValue(source, forKey: kCIInputImageKey)

    // Vary filter parameters based on video timing
    let seconds = CMTimeGetSeconds(request.compositionTime)
    filter.setValue(seconds * 10.0, forKey: kCIInputRadiusKey)

    // Crop the blurred output to the bounds of the original image
    let output = filter.outputImage!.imageByCroppingToRect(request.sourceImage.extent)

    // Provide the filter output to the composition
    request.finishWithImage(output, context: nil)
})

tutorial in Objective C 也可能是一个很好的资源。