合并视频，但AVAssetExportSession永远无法完成

Question

尝试将一些视频合并并导出为单个文件，查看教程/示例后一切似乎都是正确的，但我的AVAssetExportSession似乎永远不会完成，我的视频文件也从未被导出。如果您能帮忙找出我所忽略的明显错误，将不胜感激。

以下是合并视频的函数：

注意：循环中的'videos'是一个成员变量'var videos = [AVAsset]()'，在调用合并函数之前已经被填充（我已经检查过）。

private func merge()
{
    // Create AVMutableComposition to contain all AVMutableComposition tracks
    var mix_composition = AVMutableComposition()
    var total_time_seconds  = 0.0
    var tracks = [AVCompositionTrack]()

    // Loop over videos and create tracks, keep incrementing total duration
    for video in videos
    {
        // Create the composition track for this video
        let track = mix_composition.addMutableTrackWithMediaType(AVMediaTypeVideo, preferredTrackID: Int32(kCMPersistentTrackID_Invalid))

        // Add video duration to total time
        total_time_seconds = total_time_seconds + video.duration.seconds

        // Add track to array of tracks
        tracks.append(track)

        // Add time range to track
        do
        {
            try track.insertTimeRange(CMTimeRangeMake(kCMTimeZero, video.duration), ofTrack: video.tracksWithMediaType(AVMediaTypeVideo)[0], atTime: video.duration)
        }
        catch _
        {
        }
    }

    // Set total time
    let preferred_time_scale: Int32 = 600;
    let total_time = CMTimeMakeWithSeconds(total_time_seconds, preferred_time_scale)

    // Create main instrcution for video composition
    let main_instruction = AVMutableVideoCompositionInstruction()
    main_instruction.timeRange = CMTimeRangeMake(kCMTimeZero, total_time)

    // Create array to hold instructions
    var layer_instructions = [AVVideoCompositionLayerInstruction]()

    // Ensure we have the same number of tracks as videos
    if videos.count == tracks.count
    {
        // Loop number of videos and tracks
        for var index = 0; index < videos.count; ++index
        {
            // Create compositioninstruction for each track
            let instruction = videoCompositionInstructionForTrack(tracks[index], asset: videos[index])

            if(index == 0)
            {
                instruction.setOpacity(0.0, atTime: videos[index].duration)
            }

            // Add instruction to instructions array
            layer_instructions.append(instruction)
        }
    }

    // Set tack instructions to main instruction
    main_instruction.layerInstructions = layer_instructions
    let main_composition = AVMutableVideoComposition()
    main_composition.instructions = [main_instruction]
    main_composition.frameDuration = CMTimeMake(1, 30)
    main_composition.renderSize = CGSize(width: UIScreen.mainScreen().bounds.width, height: UIScreen.mainScreen().bounds.height)

    // Get path for Final video in the current project directory
    let documents_url = NSFileManager.defaultManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask)[0]
    let final_url = documents_url.URLByAppendingPathComponent("TEST.mp4")

    // Create AV Export Session
    let exporter = AVAssetExportSession(asset: mix_composition, presetName: AVAssetExportPresetHighestQuality)
    exporter!.outputURL = final_url
    exporter!.outputFileType = AVFileTypeMPEG4
    exporter!.shouldOptimizeForNetworkUse = true
    exporter!.videoComposition = main_composition

    // Perform the Export
    exporter!.exportAsynchronouslyWithCompletionHandler() {
        dispatch_async(dispatch_get_main_queue(), { () -> Void in
            self.exportDidFinish(exporter!)
        })
    }
}

下面展示了exportDidFinished函数，当调用exportAsynchronouslyWithCompletionHandler时会被调用。我进入了这个函数，但是因为会话状态从未完成，所以什么也没有发生。

func exportDidFinish(session: AVAssetExportSession)
{
    if session.status == AVAssetExportSessionStatus.Completed
    {
        let outputURL = session.outputURL
        let library = ALAssetsLibrary()
        if library.videoAtPathIsCompatibleWithSavedPhotosAlbum(outputURL)
        {
            library.writeVideoAtPathToSavedPhotosAlbum(outputURL,
                completionBlock: { (assetURL:NSURL!, error:NSError!) -> Void in
                    if error != nil
                    {
                        let alert = UIAlertView(title: "Error", message: "Video Not Saved", delegate: nil, cancelButtonTitle: "OK")
                        alert.show()

                    }
                    else
                    {
                        let alert = UIAlertView(title: "Success", message: "Video Saved", delegate: nil, cancelButtonTitle: "OK")
                        alert.show()
                    }
            })
        }
    }
}

打印会话状态显示为4，表示失败。因此，我打印了session.error并得到了以下内容，但我不确定它的含义，希望能得到帮助。

Optional(Error Domain=AVFoundationErrorDomain Code=-11841 "Operation Stopped" UserInfo={NSLocalizedDescription=Operation Stopped, NSLocalizedFailureReason=The video could not be composed.}) 

- AngryDuck

Answer 1

如果调用了exportDidFinish但没有任何反应，那么您的会话状态不是AVAssetExportSessionStatus.Completed。它可能是AVAssetExportSessionStatus.Failed或其他值。请检查这些值，如果失败，请检查session.error属性以获取更多信息。

编辑：如果您想让一个视频在另一个视频之后播放，请仅创建一个AVMutableCompositionTrack。有关相关更改，请参见下文：

    ...
    var mix_composition = AVMutableComposition()

    // Create the composition track for the videos
    let track = mix_composition.addMutableTrackWithMediaType(AVMediaTypeVideo, preferredTrackID: Int32(kCMPersistentTrackID_Invalid))

    //keep track of total time
    var totalTime = kCMTimeZero

    for video in videos
    {
        // Add time range to track
        do
        {
            let videoTrack = video.tracksWithMediaType(AVMediaTypeVideo)[0]
            let videoDuration = videoTrack.duration
            let timeRange = CMTimeRangeMake(kCMTimeZero,videoDuration)

            try track.insertTimeRange(timeRange, ofTrack: videoTrack, atTime: totalTime)

            totalTime = CMTimeAdd(totalTime,videoDuration)
        }
        catch _
        {
        }
    }

    // Create main instruction for video composition
    let main_instruction = AVMutableVideoCompositionInstruction()
    main_instruction.timeRange = CMTimeRangeMake(kCMTimeZero, totalTime)

    // Create array to hold instructions
    var layer_instructions = [AVVideoCompositionLayerInstruction]()

    // Create layer instruction
    let layerInstruction = AVMutableVideoCompositionLayerInstruction(assetTrack: track)

    // Add it to the array
    layer_instructions.append(layerInstruction)

    ...

您还需要将renderSize调整为适当的大小。您的视频大小可能不是屏幕大小。

- jlw

---

我如何实际检查我打印的值？状态输出了"AVAssetExportSessionStatus"，但这只是一个字符串。 - AngryDuck

print(session!.status.rawValue)。然后打印(session!.error)。 - jlw

好的，所以状态码是4，表示失败，并且我收到了这个错误信息：“Optional(Error Domain=AVFoundationErrorDomain Code=-11841 "Operation Stopped" UserInfo={NSLocalizedDescription=Operation Stopped, NSLocalizedFailureReason=The video could not be composed.})”。 - AngryDuck

我今晚会试一下，并告诉你结果，感谢你的回答。 - AngryDuck