ios - 设置 AVMutableVideoComposition 指令导致处理程序不被调用

Question

我有一个过滤 AVPlayerItem Assets 的功能。问题之一是设置视频的转换。但是，每当我设置 AVMutableVideoComposition 的 AVMutableVideoCompositionInstruction 时，处理程序就不再被调用。

这是我的代码:

private func filter(playerItem: AVPlayerItem) {

    let videoComposition = AVMutableVideoComposition(asset: playerItem.asset, applyingCIFiltersWithHandler: { (request) in
        print("Composing") // does not print whenever the instructions are added
        if let filteredImage = filterImage(request.sourceImage) {
            request.finish(with: filteredImage, context: nil)
        } else {
            request.finish(with: RenderError.couldNotFilter) // An error
        }
    })

    guard let videoTrack = playerItem.asset.tracks(withMediaType: .video).first else { return }

    let size = CGSize(width: videoTrack.naturalSize.height, height: videoTrack.naturalSize.width)
    videoComposition.renderSize = size

    let videoInstruction = AVMutableVideoCompositionInstruction()
    videoInstruction.timeRange = CMTimeRange(start: kCMTimeZero, duration: playerItem.asset.duration)

    let transformInstruction = AVMutableVideoCompositionLayerInstruction(assetTrack: videoTrack)
    let translate = CGAffineTransform(translationX: size.width, y: size.height)
    let rotate = CGAffineTransform(rotationAngle: CGFloat.pi)
    transformInstruction.setTransform(translate.concatenating(rotate), at: kCMTimeZero)
    videoInstruction.layerInstructions.append(transformInstruction)
    videoComposition.instructions.append(videoInstruction)

    playerItem.videoComposition = videoComposition
}

为什么不再调用处理程序，我该如何解决？

_{如果你能回答我就给你这么多加分!}

Answer 1

我向 Apple 提交了错误报告，显然这种行为不是错误。这是他们的回应:

Engineering has provided the following information regarding this issue:

CoreImage filtering and layer instruction based composition can't be used simultaneously. Layer instructions won't be run when added to an AVMutableVideoComposition that it is initialized with +[videoCompositionWithAsset:applyingCIFiltersWithHandler:]. To use layer instructions in this case, move the functionality into the handler instead of adding the layer instructions to the AVMutableVideoComposition.

这解释了为什么指令似乎没有做任何事情，并且没有调用处理程序。他们说将转换功能移至处理程序而不是使用指令；不幸的是，我不太清楚如何实现这个解决方案——那是另一个问题。