在之前的兩篇文章中，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。以及通過? AVMutableComposition?來將多段視頻片段的視頻、音頻軌道進行拼接合成。 Swift - 視頻錄制教程1（調用攝像頭錄像，并保存到系統相冊）
Swift - 視頻錄制教程2（小視頻拍攝，將多段視頻進行合并） 這兩個樣例我們用的都是全屏錄像，拍攝下的視頻是豎的（iPhone6拍攝的分辨率是1080*1920）。

但我們看市面上常見的視頻APP，拍攝的小視頻都是正方形，或者是橫向的矩形。本文演示如何修改視頻拍攝尺寸，這里以實現正方形視頻的拍攝為例。

1，要實現正方形視頻的拍攝要從下面幾方面入手：
（1）預覽窗口（ AVCaptureVideoPreviewLayer）尺寸設置為正方矩形（長寬均為屏幕寬度），并在整個屏幕垂直居中。
（2）視頻片段錄制的時候還是使用完整的分辨率尺寸進行錄制。
（3）在將各個視頻片段合并輸出時，我們通過? AVMutableVideoComposition?實現視頻的裁剪，即從視頻的中央位置裁出一個正方形的內容并保存文件。
2，效果圖如下： ? ? ? ? ?
3，樣例代碼

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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() ????????? ???????? //背景色設為黑色 ???????? self .view.backgroundColor =? UIColor .blackColor() ????????? ???????? //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) ???????? //預覽窗口是正方形，在屏幕居中（顯示的也是攝像頭拍攝的中心區域） ???????? videoLayer.frame =? CGRectMake (0,? self .view.bounds.height/4, ?????????????????????????????????????? self .view.bounds.width,? self .view.bounds.width) ???????? videoLayer.videoGravity =? AVLayerVideoGravityResizeAspectFill ???????? videoLayer.pointForCaptureDevicePointOfInterest( CGPoint (x: 0, y: 0)) ???????? 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，自動合并視頻 ???????? 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() ???? } ????? ???? //合并視頻片段 ???? func? mergeVideos() { ???????? let? duration = totalSeconds ????????? ???????? let? composition =? AVMutableComposition () ???????? //合并視頻、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 ( "合并視頻片段：\(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 )) ????????? ???????? //定義最終生成的視頻尺寸（矩形的） ???????? print ( "視頻原始尺寸：" , firstTrack.naturalSize) ???????? let? renderSize =? CGSizeMake (firstTrack.naturalSize.height, firstTrack.naturalSize.height) ???????? print ( "最終渲染尺寸：" , renderSize) ????????? ???????? //通過AVMutableVideoComposition實現視頻的裁剪(矩形，截取正中心區域視頻) ???????? let? videoComposition =? AVMutableVideoComposition () ???????? videoComposition.frameDuration =? CMTimeMake (1, framesPerSecond) ???????? videoComposition.renderSize = renderSize ????????? ???????? let? instruction =? AVMutableVideoCompositionInstruction () ???????? instruction.timeRange =? CMTimeRangeMake ( ???????????? kCMTimeZero, CMTimeMakeWithSeconds ( Float64 (duration), framesPerSecond)) ????????? ???????? let? transformer:? AVMutableVideoCompositionLayerInstruction? = ???????????? AVMutableVideoCompositionLayerInstruction (assetTrack: firstTrack) ???????? let? t1 =? CGAffineTransformMakeTranslation (firstTrack.naturalSize.height, ???????????????????? -(firstTrack.naturalSize.width-firstTrack.naturalSize.height)/2) ???????? let? t2 =? CGAffineTransformRotate (t1,? CGFloat ( M_PI_2 )) ???????? let? finalTransform:? CGAffineTransform? = t2 ???????? transformer.setTransform(finalTransform, atTime: kCMTimeZero) ????????? ???????? instruction.layerInstructions = [transformer] ???????? videoComposition.instructions = [instruction] ????????? ???????? //獲取合并后的視頻路徑 ???????? let? documentsPath =? NSSearchPathForDirectoriesInDomains (. DocumentDirectory , ???????????????????????????????????????????????????????????????? . UserDomainMask , true )[0] ???????? let? destinationPath = documentsPath +? "/mergeVideo-\(arc4random()%1000).mov" ???????? print ( "合并后的視頻：\(destinationPath)" ) ???????? let? videoPath:? NSURL? =? NSURL (fileURLWithPath: destinationPath? as? String ) ???????? let? exporter =? AVAssetExportSession (asset: composition, ???????????????????????????????????????????? presetName: AVAssetExportPresetHighestQuality )! ???????? exporter.outputURL = videoPath ???????? exporter.outputFileType =? AVFileTypeQuickTimeMovie ???????? exporter.videoComposition = videoComposition? //設置videoComposition ???????? exporter.shouldOptimizeForNetworkUse =? true ???????? exporter.timeRange =? CMTimeRangeMake ( ???????????? kCMTimeZero, CMTimeMakeWithSeconds ( Float64 (duration), framesPerSecond)) ???????? exporter.exportAsynchronouslyWithCompletionHandler({ ???????????? //將合并后的視頻保存到相冊 ???????????? self .exportDidFinish(exporter) ???????? }) ???? } ????? ???? //將合并后的視頻保存到相冊 ???? func? exportDidFinish(session:? AVAssetExportSession ) { ???????? print ( "視頻合并成功！" ) ???????? 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，準備新視頻錄制 ???? 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() ???????? } ???? } }

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