前面介紹過一篇視頻錄制的教程這裡接著來看一篇關於Swift 視頻錄制之小視頻拍攝，將多段視頻進行合並的例子。

我介紹了如何通過 AVFoundation.framework 框架提供的 AVCaptureSession 類來實現視頻的錄制。
當時的程序是點擊“開始”按鈕就開始視頻錄制，點擊“停止”則將視頻保存起來。整個視頻是連續地錄制，沒有時間限制。今天繼續在其基礎之上做個改進，實現小視頻拍攝功能。

1，小視頻拍攝要實現的功能
（1）視頻可以分段錄制。按住“錄像”按鈕，則開始捕獲攝像頭進行視頻錄制，放開按鈕則暫停錄制。
（2）所有視頻片段加起來的時間長度會有限制（本樣例限制為15秒）。錄制的時候頂部會有實時的進度條。
（3）點擊“保存”按鈕，或者總時長到達15秒時，則停止繼續錄像。程序會將各個視頻片段進行合並，並保存到系統相冊中。
（4）保存成功後，可以回看生成的錄像。

2，效果圖如下

3，實現原理

（1）每次按下按鈕錄制的視頻片段，同樣是使用 AVCaptureMovieFileOutput 輸出到 Documents 文件夾下，命名為 output-1.mov、output-2.mov....
（2）通過 AVMutableComposition 來拼接合成各個視頻片段的視頻、音頻軌道。
（3）使用 AVAssetExportSession 將合並後的視頻壓縮輸出成一個最終的視頻文件：mergeVideo-****.mov（本文使用高質量壓縮），並保存到系統相冊中去。
（4）通過 AVPlayerViewController 進行錄像的回看。

4，錄制一段由三個片段合成的視頻，控制台信息如下：

5，樣例代碼

import UIKit
import AVFoundation
import Photos
import AVKit
 
class ViewController: UIViewController , AVCaptureFileOutputRecordingDelegate {
    
    //視頻捕獲會話。它是input和output的橋梁。它協調著intput到output的數據傳輸
    let captureSession = AVCaptureSession()
    //視頻輸入設備
    let videoDevice = AVCaptureDevice.defaultDeviceWithMediaType(AVMediaTypeVideo)
    //音頻輸入設備
    let audioDevice = AVCaptureDevice.defaultDeviceWithMediaType(AVMediaTypeAudio)
    //將捕獲到的視頻輸出到文件
    let fileOutput = AVCaptureMovieFileOutput()
    
    //錄制、保存按鈕
    var recordButton, saveButton : UIButton!
    
    //保存所有的錄像片段數組
    var videoAssets = [AVAsset]()
    //保存所有的錄像片段url數組
    var assetURLs = [String]()
    //單獨錄像片段的index索引
    var appendix: Int32 = 1
    
    //最大允許的錄制時間（秒）
    let totalSeconds: Float64 = 15.00
    //每秒幀數
    var framesPerSecond:Int32 = 30
    //剩余時間
    var remainingTime : NSTimeInterval = 15.0
    
    //表示是否停止錄像
    var stopRecording: Bool = false
    //剩余時間計時器
    var timer: NSTimer?
    //進度條計時器
    var progressBarTimer: NSTimer?
    //進度條計時器時間間隔
    var incInterval: NSTimeInterval = 0.05
    //進度條
    var progressBar: UIView = UIView()
    //當前進度條終點位置
    var oldX: CGFloat = 0
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        //添加視頻、音頻輸入設備
        let videoInput = try! AVCaptureDeviceInput(device: self.videoDevice)
        self.captureSession.addInput(videoInput)
        let audioInput = try! AVCaptureDeviceInput(device: self.audioDevice)
        self.captureSession.addInput(audioInput);
        
        //添加視頻捕獲輸出
        let maxDuration = CMTimeMakeWithSeconds(totalSeconds, framesPerSecond)
        self.fileOutput.maxRecordedDuration = maxDuration
        self.captureSession.addOutput(self.fileOutput)
        
        //使用AVCaptureVideoPreviewLayer可以將攝像頭的拍攝的實時畫面顯示在ViewController上
        let videoLayer = AVCaptureVideoPreviewLayer(session: self.captureSession)
        videoLayer.frame = self.view.bounds
        videoLayer.videoGravity = AVLayerVideoGravityResizeAspectFill
        self.view.layer.addSublayer(videoLayer)
        
        //創建按鈕
        self.setupButton()
        //啟動session會話
        self.captureSession.startRunning()
        
        //添加進度條
        progressBar.frame = CGRect(x: 0, y: 0, width: self.view.bounds.width,
                                   height: self.view.bounds.height * 0.1)
        progressBar.backgroundColor = UIColor(red: 4, green: 3, blue: 3, alpha: 0.5)
        self.view.addSubview(progressBar)
    }
    
    //創建按鈕
    func setupButton(){
        //創建錄制按鈕
        self.recordButton = UIButton(frame: CGRectMake(0,0,120,50))
        self.recordButton.backgroundColor = UIColor.redColor();
        self.recordButton.layer.masksToBounds = true
        self.recordButton.setTitle("按住錄像", forState: .Normal)
        self.recordButton.layer.cornerRadius = 20.0
        self.recordButton.layer.position = CGPoint(x: self.view.bounds.width/2,
                                                   y:self.view.bounds.height-50)
        self.recordButton.addTarget(self, action: #selector(onTouchDownRecordButton(_:)),
                                    forControlEvents: .TouchDown)
        self.recordButton.addTarget(self, action: #selector(onTouchUpRecordButton(_:)),
                                    forControlEvents: .TouchUpInside)
        
        //創建保存按鈕
        self.saveButton = UIButton(frame: CGRectMake(0,0,70,50))
        self.saveButton.backgroundColor = UIColor.grayColor();
        self.saveButton.layer.masksToBounds = true
        self.saveButton.setTitle("保存", forState: .Normal)
        self.saveButton.layer.cornerRadius = 20.0
        
        self.saveButton.layer.position = CGPoint(x: self.view.bounds.width - 60,
                                                 y:self.view.bounds.height-50)
        self.saveButton.addTarget(self, action: #selector(onClickStopButton(_:)),
                                  forControlEvents: .TouchUpInside)
        
        //添加按鈕到視圖上
        self.view.addSubview(self.recordButton);
        self.view.addSubview(self.saveButton);
    }
    
    //按下錄制按鈕，開始錄制片段
    func  onTouchDownRecordButton(sender: UIButton){
        if(!stopRecording) {
            let paths = NSSearchPathForDirectoriesInDomains(.DocumentDirectory,
                                                            .UserDomainMask, true)
            let documentsDirectory = paths[0] as String
            let outputFilePath = "\(documentsDirectory)/output-\(appendix).mov"
            appendix += 1
            let outputURL = NSURL(fileURLWithPath: outputFilePath)
            let fileManager = NSFileManager.defaultManager()
            if(fileManager.fileExistsAtPath(outputFilePath)) {
                
                do {
                    try fileManager.removeItemAtPath(outputFilePath)
                } catch _ {
                }
            }
            print("開始錄制：\(outputFilePath) ")
            fileOutput.startRecordingToOutputFileURL(outputURL, recordingDelegate: self)
        }
    }
    
    //松開錄制按鈕，停止錄制片段
    func  onTouchUpRecordButton(sender: UIButton){
        if(!stopRecording) {
            timer?.invalidate()
            progressBarTimer?.invalidate()
            fileOutput.stopRecording()
        }
    }
    
    //錄像開始的代理方法
    func captureOutput(captureOutput: AVCaptureFileOutput!,
                       didStartRecordingToOutputFileAtURL fileURL: NSURL!,
                        fromConnections connections: [AnyObject]!) {
        startProgressBarTimer()
        startTimer()
    }
    
    //錄像結束的代理方法
    func captureOutput(captureOutput: AVCaptureFileOutput!,
                       didFinishRecordingToOutputFileAtURL outputFileURL: NSURL!,
                        fromConnections connections: [AnyObject]!, error: NSError!) {
        let asset : AVURLAsset = AVURLAsset(URL: outputFileURL, options: nil)
        var duration : NSTimeInterval = 0.0
        duration = CMTimeGetSeconds(asset.duration)
        print("生成視頻片段：\(asset)")
        videoAssets.append(asset)
        assetURLs.append(outputFileURL.path!)
        remainingTime = remainingTime - duration
        
        //到達允許最大錄制時間，自動合並視頻
        if remainingTime <= 0 {
            mergeVideos()
        }
    }
    
    //剩余時間計時器
    func startTimer() {
        timer = NSTimer(timeInterval: remainingTime, target: self,
                        selector: #selector(ViewController.timeout), userInfo: nil,
                        repeats:true)
        NSRunLoop.currentRunLoop().addTimer(timer!, forMode: NSDefaultRunLoopMode)
    }
    
    //錄制時間達到最大時間
    func timeout() {
        stopRecording = true
        print("時間到。")
        fileOutput.stopRecording()
        timer?.invalidate()
        progressBarTimer?.invalidate()
    }
    
    //進度條計時器
    func startProgressBarTimer() {
        progressBarTimer = NSTimer(timeInterval: incInterval, target: self,
                                   selector: #selector(ViewController.progress),
                                   userInfo: nil, repeats: true)
        NSRunLoop.currentRunLoop().addTimer(progressBarTimer!,
                                            forMode: NSDefaultRunLoopMode)
    }
    
    //修改進度條進度
    func progress() {
        let progressProportion: CGFloat = CGFloat(incInterval / totalSeconds)
        let progressInc: UIView = UIView()
        progressInc.backgroundColor = UIColor(red: 55/255, green: 186/255, blue: 89/255,
                                              alpha: 1)
        let newWidth = progressBar.frame.width * progressProportion
        progressInc.frame = CGRect(x: oldX , y: 0, width: newWidth,
                                   height: progressBar.frame.height)
        oldX = oldX + newWidth
        progressBar.addSubview(progressInc)
    }
    
    //保存按鈕點擊
    func onClickStopButton(sender: UIButton){
        mergeVideos()
    }
    
    //合並視頻片段
    func mergeVideos() {
        let duration = totalSeconds
        
        let composition = AVMutableComposition()
        //合並視頻、音頻軌道
        let firstTrack = composition.addMutableTrackWithMediaType(
            AVMediaTypeVideo, preferredTrackID: CMPersistentTrackID())
        let audioTrack = composition.addMutableTrackWithMediaType(
            AVMediaTypeAudio, preferredTrackID: CMPersistentTrackID())
        
        var insertTime: CMTime = kCMTimeZero
        for asset in videoAssets {
            print("合並視頻片段：\(asset)")
            do {
                try firstTrack.insertTimeRange(
                    CMTimeRangeMake(kCMTimeZero, asset.duration),
                    ofTrack: asset.tracksWithMediaType(AVMediaTypeVideo)[0] ,
                    atTime: insertTime)
            } catch _ {
            }
            do {
                try audioTrack.insertTimeRange(
                    CMTimeRangeMake(kCMTimeZero, asset.duration),
                    ofTrack: asset.tracksWithMediaType(AVMediaTypeAudio)[0] ,
                    atTime: insertTime)
            } catch _ {
            }
            
            insertTime = CMTimeAdd(insertTime, asset.duration)
        }
        //旋轉視頻圖像，防止90度顛倒
        firstTrack.preferredTransform = CGAffineTransformMakeRotation(CGFloat(M_PI_2))
        
        //獲取合並後的視頻路徑
        let documentsPath = NSSearchPathForDirectoriesInDomains(.DocumentDirectory,
                                                                .UserDomainMask,true)[0]
        let destinationPath = documentsPath + "/mergeVideo-\(arc4random()%1000).mov"
        print("合並後的視頻：\(destinationPath)")
        let videoPath: NSURL = NSURL(fileURLWithPath: destinationPath as String)
        let exporter = AVAssetExportSession(asset: composition,
                                            presetName:AVAssetExportPresetHighestQuality)!
        exporter.outputURL = videoPath
        exporter.outputFileType = AVFileTypeQuickTimeMovie
        exporter.shouldOptimizeForNetworkUse = true
        exporter.timeRange = CMTimeRangeMake(
            kCMTimeZero,CMTimeMakeWithSeconds(Float64(duration), framesPerSecond))
        exporter.exportAsynchronouslyWithCompletionHandler({
            //將合並後的視頻保存到相冊
            self.exportDidFinish(exporter)
        })
    }
    
    //將合並後的視頻保存到相冊
    func exportDidFinish(session: AVAssetExportSession) {
        print("視頻合並成功！")
        let outputURL: NSURL = session.outputURL!
        //將錄制好的錄像保存到照片庫中
        PHPhotoLibrary.sharedPhotoLibrary().performChanges({
            PHAssetChangeRequest.creationRequestForAssetFromVideoAtFileURL(outputURL)
            }, completionHandler: { (isSuccess: Bool, error: NSError?) in
                dispatch_async(dispatch_get_main_queue(),{
                    //重置參數
                    self.reset()
                    
                    //彈出提示框
                    let alertController = UIAlertController(title: "視頻保存成功",
                        message: "是否需要回看錄像？", preferredStyle: .Alert)
                    let okAction = UIAlertAction(title: "確定", style: .Default, handler: {
                        action in
                        //錄像回看
                        self.reviewRecord(outputURL)
                    })
                    let cancelAction = UIAlertAction(title: "取消", style: .Cancel,
                        handler: nil)
                    alertController.addAction(okAction)
                    alertController.addAction(cancelAction)
                    self.presentViewController(alertController, animated: true,
                        completion: nil)
                })
        })
    }
    
    //視頻保存成功，重置各個參數，准備新視頻錄制
    func reset() {
        //刪除視頻片段
        for assetURL in assetURLs {
            if(NSFileManager.defaultManager().fileExistsAtPath(assetURL)) {
                do {
                    try NSFileManager.defaultManager().removeItemAtPath(assetURL)
                } catch _ {
                }
                print("刪除視頻片段: \(assetURL)")
            }
        }
        
        //進度條還原
        let subviews = progressBar.subviews
        for subview in subviews {
            subview.removeFromSuperview()
        }
        
        //各個參數還原
        videoAssets.removeAll(keepCapacity: false)
        assetURLs.removeAll(keepCapacity: false)
        appendix = 1
        oldX = 0
        stopRecording = false
        remainingTime = totalSeconds
    }
    
    //錄像回看
    func reviewRecord(outputURL: NSURL) {
        //定義一個視頻播放器，通過本地文件路徑初始化
        let player = AVPlayer(URL: outputURL)
        let playerViewController = AVPlayerViewController()
        playerViewController.player = player
        self.presentViewController(playerViewController, animated: true) {
            playerViewController.player!.play()
        }
    }
}