AVAssetExportSession导出失败非确定性错误:"操作已停止,NSLocalizedFailureReason =视频无法合成."

Question

我们为用户录制的视频添加了字幕,但AVAssetExportSession对象的导出失败是非确定性的:有时它会起作用,有时它不起作用.目前还不清楚如何重现错误.

我们注意到出口期间资产跟踪似乎丢失了.

在导出之前,有两个轨道(一个用于音频,一个用于视频),如预期的那样.但是在exportDidFinish显示0个曲目中检查相同文件URL的曲目数.所以出口过程似乎有些问题.

更新:注释会exporter.videoComposition = mutableComposition修复错误,但当然不会对视频应用任何转换.所以问题似乎在于创造AVMutableVideoComposition,这会在出口期间导致下游问题.文档和教程AVMutableVideoComposition很少,所以即使您没有解决方案但可以推荐Apple以外的参考资料,这将有所帮助.

错误:

Error Domain = AVFoundationErrorDomain Code = -11841"Operation Stopped"UserInfo = 0x170676e80 {NSLocalizedDescription = Operation Stopped,NSLocalizedFailureReason =视频无法合成.}

码:

    let videoAsset = AVURLAsset(URL: fileUrl, options: nil)
    let mixComposition = AVMutableComposition()
    let videoTrack = mixComposition.addMutableTrackWithMediaType(AVMediaTypeVideo, preferredTrackID: CMPersistentTrackID(kCMPersistentTrackID_Invalid))
    let audioTrack = mixComposition.addMutableTrackWithMediaType(AVMediaTypeAudio, preferredTrackID: CMPersistentTrackID(kCMPersistentTrackID_Invalid))

    let sourceVideoTrack = videoAsset.tracksWithMediaType(AVMediaTypeVideo)[0] as! AVAssetTrack
    let sourceAudioTrack = videoAsset.tracksWithMediaType(AVMediaTypeAudio)[0] as! AVAssetTrack
    videoTrack.insertTimeRange(CMTimeRangeMake(kCMTimeZero, videoAsset.duration), ofTrack: sourceVideoTrack, atTime: kCMTimeZero, error: nil)
    audioTrack.insertTimeRange(CMTimeRangeMake(kCMTimeZero, videoAsset.duration), ofTrack: sourceAudioTrack, atTime: kCMTimeZero, error: nil)

    // Create something mutable???
    // -- Create instruction
    let instruction = AVMutableVideoCompositionInstruction()
    instruction.timeRange = CMTimeRangeMake(kCMTimeZero, videoAsset.duration)
    let videoLayerInstruction = AVMutableVideoCompositionLayerInstruction(assetTrack: sourceVideoTrack)
    instruction.layerInstructions = [videoLayerInstruction]

    let mutableComposition = AVMutableVideoComposition()
    //mutableComposition.renderSize = videoTrack.naturalSize
    mutableComposition.renderSize = CGSize(width: 320, height: 320)
    mutableComposition.frameDuration = CMTimeMake(1, 60)
    mutableComposition.instructions = [instruction]

    // Animate
    mutableComposition.animationTool = AVVideoCompositionCoreAnimationTool(postProcessingAsVideoLayer: videoLayer, inLayer: parentLayer)

    // -- Get path
    let fileName = "/editedVideo-\(arc4random() % 10000).mp4"
    let allPaths = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)
    let docsPath = allPaths[0] as! NSString
    let exportPath = docsPath.stringByAppendingFormat(fileName)
    let exportUrl = NSURL.fileURLWithPath(exportPath as String)!

    println("Tracks before export: \(mixComposition.tracks.count). File URL: \(exportUrl)")

    // -- Remove old video?
    if NSFileManager.defaultManager().fileExistsAtPath(exportPath as String) {
        println("Deleting existing file\n")
        NSFileManager.defaultManager().removeItemAtPath(exportPath as String, error: nil)
    }

    // -- Create exporter
    let exporter = AVAssetExportSession(asset: mixComposition, presetName: AVAssetExportPresetHighestQuality)
    exporter.videoComposition = mutableComposition
    exporter.outputFileType = AVFileTypeMPEG4
    exporter.outputURL = exportUrl
    exporter.shouldOptimizeForNetworkUse = true

    // -- Export video
    exporter.exportAsynchronouslyWithCompletionHandler({
        self.exportDidFinish(exporter)
    })


func exportDidFinish(exporter: AVAssetExportSession) {
    println("Exported video with status: \(getExportStatus(exporter))")

    // Save video to photo album
    let assetLibrary = ALAssetsLibrary()
    assetLibrary.writeVideoAtPathToSavedPhotosAlbum(exporter.outputURL, completionBlock: {(url: NSURL!, error: NSError!) in
        println("Saved video to album \(exporter.outputURL)")
        if (error != nil) {
            println("Error saving video")
        }
    })

    // Check asset tracks
    let asset = AVAsset.assetWithURL(exporter.outputURL) as? AVAsset
    println("Tracks after export: \(asset!.tracks.count). File URL: \(exporter.outputURL)")
}

问题:

1)导致问题的原因是什么,解决方案是什么？

2)关于如何一致地重现错误的建议,希望有助于调试问题？

Answer 1

似乎是治愈方法是确保assetTrack参数AVMutableVideoCompositionLayerInstruction不是来自AVURLAsset对象,而是来自返回的视频对象addMutableTrackWithMediaType.

换句话说,这一行:

let videoLayerInstruction = AVMutableVideoCompositionLayerInstruction(assetTrack: sourceVideoTrack)

应该:

let videoLayerInstruction = AVMutableVideoCompositionLayerInstruction(assetTrack: videoTrack)

哎呀.几个小时无尽的挫败感,因为有时第一条线路有效,有时却没有.

仍然想将赏金奖励给某人.

如果您可以解释为什么第一行不确定地失败,而不是每次都失败,或者提供更深入的AVMutableComposition及其相关类的教程 - 为了向用户录制的视频添加文本叠加 - 赏金就是你的全部.:)

Answer 2

我通过使用AVAssetExportPresetPassthrough导出预设而不是使用特定分辨率解决了这个问题，或者AVAssetExportHighestQuality……

let exportSession = AVAssetExportSession(asset: composition, presetName: AVAssetExportPresetPassthrough)

这应该使用导出文件中导入视频的分辨率。

Answer 3

我猜你的一些视频sourceVideoTrack是:

• 不连续的曲目
• 时间范围短于视频整个时间范围的曲目

videoTrack另一方面,可变轨道保证了正确的时间范围(按照指示AVMutableVideoCompositionInstruction),因此它始终有效.