如何提高 AVAssetExportSession 保存性能

Posted 2023-03-08

【中文标题】如何提高 AVAssetExportSession 保存性能

【英文标题】：How to improve AVAssetExportSession saving performance

【发布时间】：2020-12-19 12:21:12

【问题描述】：

我正在使用AVAssetExportSession 保存带有一些文本/图像覆盖的视频。 它工作得很好，除了保存新视频需要很多时间，我见过其他应用程序做得更快，比如快 2-4 倍。所以我想知道我做错了什么吗？

这是我的代码（我删除了一些不相关的部分以便更好地阅读错误，如果您想查看某些功能的实现，请告诉我）：

 func saveVideo() 
    guard let fileURL = videoMediaURL else  return 

    let vidAsset = AVURLAsset(url: fileURL, options: nil)

    // Create an AVMutableComposition for editing
    let mutableComposition = getVideoComposition(asset: vidAsset)

    let videoTrack: AVAssetTrack = mutableComposition.tracks(withMediaType: AVMediaType.video)[0]
    var size = videoTrack.naturalSize

    //fixing native ios rotated video
    if videoTrack.preferredTransform.c == -1 
        size = CGSize(width: size.height, height: size.width)
    

    let isLandscape = size.width > size.height
    if videoTrack.preferredTransform.a == 1 && videoTrack.preferredTransform.d == 1 && isLandscape 
        size = CGSize(width: size.height, height: size.width)
    

    let instruction = AVMutableVideoCompositionInstruction()
    instruction.timeRange = CMTimeRangeMake(start: CMTime.zero, duration: mutableComposition.duration)
    let layerInstruction = AVMutableVideoCompositionLayerInstruction(assetTrack: videoTrack)

    var transform = videoTrack.preferredTransform

    if transform.a == 1 && transform.d == 1 && isLandscape 
        let diff = size.height / size.width
        let scale = videoTrack.preferredTransform.xScale * diff
        transform = videoTrack.preferredTransform.translatedBy(x: (-size.width * scale) / 1.65, y: videoTrack.preferredTransform.yOffset).scaledBy(x: videoTrack.preferredTransform.xScale * diff, y: videoTrack.preferredTransform.yScale * diff)
    

    if transform.tx >= 3840 
        transform = videoTrack.preferredTransform.translatedBy(x: 0, y: transform.xOffset / 2)
    

    layerInstruction.setTransform(transform, at: .zero)
    instruction.layerInstructions = [layerInstruction]


    let containerLayer = setupLayers()

    let layerComposition = AVMutableVideoComposition()
    layerComposition.frameDuration = CMTimeMake(value: 1, timescale: Int32(videoTrack.nominalFrameRate))
    layerComposition.renderSize = size
    layerComposition.animationTool = AVVideoCompositionCoreAnimationTool(postProcessingAsVideoLayer: videoLayer, in: containerLayer)
    layerComposition.instructions = [instruction]

    //Remove existing file
    deleteFile(outputURL)

    //export the video to as per your requirement conversion
    if let exportSession = AVAssetExportSession(asset: mutableComposition, presetName: AVAssetExportPresetHighestQuality) 
        self.exportSession = exportSession
        exportSession.outputURL = outputURL
        exportSession.outputFileType = AVFileType.m4v
        exportSession.shouldOptimizeForNetworkUse = true
        exportSession.videoComposition = layerComposition
        // try to export the file and handle the status cases
        exportSession.exportAsynchronously(completionHandler: 
            //handle exportSession result

        )
    

【问题讨论】：

是不是因为AVAssetExportPresetHighestQuality？

@matt 我必须提供高质量的视频，所以不能设置较低的质量。我仍然可以看到其他更快地导出高质量视频的应用

导出需要多长时间？您有示例输入和输出文件吗？

@RhythmicFistman 10 秒 4k 视频大约需要 10 秒，我可以上传示例输入/输出视频

@RhythmicFistman dropbox.com/sh/g9lfxqtolh8m6xq/AAC7T2jQbTVr4lh03W5bxOz1a?dl=0

【参考方案1】：

我正在用AVAssetExportSession 追查这个问题，它可能与这个AVAssetExportSession never starts on older devices, device needs to be rebooted 相关联。

您是否能够解决您的问题？我在问，因为这两个问题及时接近，可能是由 iOS 14.3 中的错误引起的。

【讨论】：

你找到什么了吗？我在 iOS 14.3、14.4 上遇到了同样的问题