[AVFoundation-当我在视频上粘贴标签时，视频文件的大小增加了

Question

当我将图像叠加到视频时，AVFoundation正在增加视频文件的大小。我已将输出文件类型设置为mp4。有时视频文件的大小没有增加，但有时增加了约40 MB。是否有可能总是减小文件大小？

Answer 1

您应该检查在视频上粘贴标签的方式。它是动画（贴纸运动的图像）还是仅仅是图像。如果仅是单个图像，例如在开始导出会话之前，您可以执行以下操作：

    let parentLayer = CALayer()
    let videoLayer = CALayer()
    let overlayLayer = CALayer()
    let stickerLayer = CALayer()

    parentLayer.frame = CGRect(origin: .zero, size: renderSize)
    videoLayer.frame = parentLayer.frame
    stickerLayer.frame = parentLayer.frame
    overlayLayer.frame = parentLayer.bounds
    //Add the image inside of stickerLayer(in this case its from a screen shot of UIView, you can change to your custom UIImage
    stickerLayer.contents = self.stickerView.asImage().cgImage
    parentLayer.addSublayer(videoLayer)
    parentLayer.addSublayer(stickerLayer)
    parentLayer.addSublayer(overlayLayer)

    //create composition
    let videoComposition = AVMutableVideoComposition()
    videoComposition.renderSize = CGSize(width: renderSize.width, height: renderSize.height)
    videoComposition.frameDuration = CMTimeMake(value: 1, timescale: 30)
    videoComposition.renderScale = 1.0

    //finally add layers with animationTool
    videoComposition.animationTool = AVVideoCompositionCoreAnimationTool(postProcessingAsVideoLayers: [videoLayer], in: parentLayer)