在之前的两篇文章中，我介绍了如何通过 AVFoundation.framework 框架提供的 AVCaptureSession 类来实现视频的录制。以及通过 AVMutableComposition 来将多段视频片段的视频、音频轨道进行拼接合成。
Swift – 视频录制教程1（调用摄像头录像，并保存到系统相册）
Swift – 视频录制教程2（小视频拍摄，将多段视频进行合并）
这两个样例我们用的都是全屏录像，拍摄下的视频是竖的（iPhone6拍摄的分辨率是1080*1920）。
但我们看市面上常见的视频APP，拍摄的小视频都是正方形，或者是横向的矩形。本文演示如何修改视频拍摄尺寸，这里以实现正方形视频的拍摄为例。
1，要实现正方形视频的拍摄要从下面几方面入手：
- （1）预览窗口（AVCaptureVideoPreviewLayer）尺寸设置为正方矩形（长宽均为屏幕宽度），并在整个屏幕垂直居中。
- （2）视频片段录制的时候还是使用完整的分辨率尺寸进行录制。
- （3）在将各个视频片段合并输出时，我们通过 AVMutableVideoComposition 实现视频的裁剪，即从视频的中央位置裁出一个正方形的内容并保存文件。
2，效果图如下：
3，Info.plist 配置
由于苹果安全策略更新，在使用 Xcode8 开发时，需要在 Info.plist 配置请求摄像头、麦克风、相册权限的描述字段：
- Privacy – Camera Usage Description
- Privacy – Microphone Usage Description
- Privacy – Photo Library Usage Description
4，样例代码
import UIKit
import AVFoundation
import Photos
import AVKit
class ViewController: UIViewController , AVCaptureFileOutputRecordingDelegate {
//视频捕获会话。它是input和output的桥梁。它协调着intput到output的数据传输
let captureSession = AVCaptureSession()
//视频输入设备
let videoDevice = AVCaptureDevice.default(for: AVMediaType.video)
//音频输入设备
let audioDevice = AVCaptureDevice.default(for: AVMediaType.audio)
//将捕获到的视频输出到文件
let fileOutput = AVCaptureMovieFileOutput()
//录制、保存按钮
var recordButton, saveButton : UIButton!
//保存所有的录像片段数组
var videoAssets = [AVAsset]()
//保存所有的录像片段url数组
var assetURLs = [String]()
//单独录像片段的index索引
var appendix: Int32 = 1
//最大允许的录制时间（秒）
let totalSeconds: Float64 = 15.00
//每秒帧数
var framesPerSecond:Int32 = 30
//剩余时间
var remainingTime : TimeInterval = 15.0
//表示是否停止录像
var stopRecording: Bool = false
//剩余时间计时器
var timer: Timer?
//进度条计时器
var progressBarTimer: Timer?
//进度条计时器时间间隔
var incInterval: TimeInterval = 0.05
//进度条
var progressBar: UIView = UIView()
//当前进度条终点位置
var oldX: CGFloat = 0
override func viewDidLoad() {
super.viewDidLoad()
//添加视频、音频输入设备
let videoInput = try! AVCaptureDeviceInput(device: self.videoDevice!)
self.captureSession.addInput(videoInput)
let audioInput = try! AVCaptureDeviceInput(device: self.audioDevice!)
self.captureSession.addInput(audioInput)
//添加视频捕获输出
let maxDuration = CMTimeMakeWithSeconds(totalSeconds, preferredTimescale: framesPerSecond)
self.fileOutput.maxRecordedDuration = maxDuration
self.captureSession.addOutput(self.fileOutput)
//使用AVCaptureVideoPreviewLayer可以将摄像头的拍摄的实时画面显示在ViewController上
let videoLayer = AVCaptureVideoPreviewLayer(session: self.captureSession)
//预览窗口是正方形，在屏幕居中（显示的也是摄像头拍摄的中心区域）
videoLayer.frame = CGRect(x:0, y:self.view.bounds.height/4,
width: self.view.bounds.width,
height: self.view.bounds.width)
videoLayer.videoGravity = AVLayerVideoGravity.resizeAspectFill
self.view.layer.addSublayer(videoLayer)
//创建按钮
self.setupButton()
//启动session会话
self.captureSession.startRunning()
//添加进度条
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)
}
//创建按钮
func setupButton(){
//创建录制按钮
self.recordButton = UIButton(frame: CGRect(x:0,y:0,width:120,height:50))
self.recordButton.backgroundColor = UIColor.red
self.recordButton.layer.masksToBounds = true
self.recordButton.setTitle("按住录像", for: .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(_:)),
for: .touchDown)
self.recordButton.addTarget(self, action: #selector(onTouchUpRecordButton(_:)),
for: .touchUpInside)
//创建保存按钮
self.saveButton = UIButton(frame: CGRect(x:0,y:0,width:70,height:50))
self.saveButton.backgroundColor = UIColor.gray
self.saveButton.layer.masksToBounds = true
self.saveButton.setTitle("保存", for: .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(_:)),
for: .touchUpInside)
//添加按钮到视图上
self.view.addSubview(self.recordButton);
self.view.addSubview(self.saveButton);
}
//按下录制按钮，开始录制片段
@objc 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 = URL(fileURLWithPath: outputFilePath)
let fileManager = FileManager.default
if(fileManager.fileExists(atPath: outputFilePath)) {
do {
try fileManager.removeItem(atPath: outputFilePath)
} catch _ {
}
}
print("开始录制：\(outputFilePath) ")
fileOutput.startRecording(to: outputURL, recordingDelegate: self)
}
}
//松开录制按钮，停止录制片段
@objc func onTouchUpRecordButton(_ sender: UIButton){
if(!stopRecording) {
timer?.invalidate()
progressBarTimer?.invalidate()
fileOutput.stopRecording()
}
}
//录像开始的代理方法
func fileOutput(_ output: AVCaptureFileOutput,
didStartRecordingTo fileURL: URL,
from connections: [AVCaptureConnection]) {
startProgressBarTimer()
startTimer()
}
//录像结束的代理方法
func fileOutput(_ output: AVCaptureFileOutput,
didFinishRecordingTo outputFileURL: URL,
from connections: [AVCaptureConnection], error: Error?) {
let asset = AVURLAsset(url: outputFileURL, options: nil)
var duration : TimeInterval = 0.0
duration = CMTimeGetSeconds(asset.duration)
print("生成视频片段：\(asset)")
videoAssets.append(asset)
assetURLs.append(outputFileURL.path)
remainingTime = remainingTime - duration
//到达允许最大录制时间，自动合并视频
if remainingTime <= 0 {
mergeVideos()
}
}
//剩余时间计时器
func startTimer() {
timer = Timer(timeInterval: remainingTime, target: self,
selector: #selector(ViewController.timeout), userInfo: nil,
repeats:true)
RunLoop.current.add(timer!, forMode: .default)
}
//录制时间达到最大时间
@objc func timeout() {
stopRecording = true
print("时间到。")
fileOutput.stopRecording()
timer?.invalidate()
progressBarTimer?.invalidate()
}
//进度条计时器
func startProgressBarTimer() {
progressBarTimer = Timer(timeInterval: incInterval, target: self,
selector: #selector(ViewController.progress),
userInfo: nil, repeats: true)
RunLoop.current.add(progressBarTimer!, forMode: .default)
}
//修改进度条进度
@objc 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)
}
//保存按钮点击
@objc func onClickStopButton(_ sender: UIButton){
mergeVideos()
}
//合并视频片段
func mergeVideos() {
let duration = totalSeconds
let composition = AVMutableComposition()
//合并视频、音频轨道
let firstTrack = composition.addMutableTrack(
withMediaType: AVMediaType.video, preferredTrackID: CMPersistentTrackID())
let audioTrack = composition.addMutableTrack(
withMediaType: AVMediaType.audio, preferredTrackID: CMPersistentTrackID())
var insertTime: CMTime = CMTime.zero
for asset in videoAssets {
print("合并视频片段：\(asset)")
do {
try firstTrack?.insertTimeRange(
CMTimeRangeMake(start: CMTime.zero, duration: asset.duration),
of: asset.tracks(withMediaType: AVMediaType.video)[0] ,
at: insertTime)
} catch _ {
}
do {
try audioTrack?.insertTimeRange(
CMTimeRangeMake(start: CMTime.zero, duration: asset.duration),
of: asset.tracks(withMediaType: AVMediaType.audio)[0] ,
at: insertTime)
} catch _ {
}
insertTime = CMTimeAdd(insertTime, asset.duration)
}
//旋转视频图像，防止90度颠倒
firstTrack?.preferredTransform = CGAffineTransform(rotationAngle: CGFloat.pi/2)
//定义最终生成的视频尺寸（矩形的）
print("视频原始尺寸：", firstTrack!.naturalSize)
let renderSize = CGSize(width: firstTrack!.naturalSize.height,
height:firstTrack!.naturalSize.height)
print("最终渲染尺寸：", renderSize)
//通过AVMutableVideoComposition实现视频的裁剪(矩形，截取正中心区域视频)
let videoComposition = AVMutableVideoComposition()
videoComposition.frameDuration = CMTimeMake(value: 1, timescale: framesPerSecond)
videoComposition.renderSize = renderSize
let instruction = AVMutableVideoCompositionInstruction()
instruction.timeRange = CMTimeRangeMake(
start: CMTime.zero,
duration: CMTimeMakeWithSeconds(Float64(duration),
preferredTimescale: framesPerSecond))
let transformer: AVMutableVideoCompositionLayerInstruction =
AVMutableVideoCompositionLayerInstruction(assetTrack: firstTrack!)
let t1 = CGAffineTransform(translationX: firstTrack!.naturalSize.height,
y: -(firstTrack!.naturalSize.width - firstTrack!.naturalSize.height)/2)
let t2 = t1.rotated(by: CGFloat.pi/2)
let finalTransform: CGAffineTransform = t2
transformer.setTransform(finalTransform, at: CMTime.zero)
instruction.layerInstructions = [transformer]
videoComposition.instructions = [instruction]
//获取合并后的视频路径
let documentsPath = NSSearchPathForDirectoriesInDomains(.documentDirectory,
.userDomainMask,true)[0]
let destinationPath = documentsPath + "/mergeVideo-\(arc4random()%1000).mov"
print("合并后的视频：\(destinationPath)")
let videoPath = URL(fileURLWithPath: destinationPath as String)
let exporter = AVAssetExportSession(asset: composition,
presetName:AVAssetExportPresetHighestQuality)!
exporter.outputURL = videoPath
exporter.outputFileType = AVFileType.mov
exporter.videoComposition = videoComposition //设置videoComposition
exporter.shouldOptimizeForNetworkUse = true
exporter.timeRange = CMTimeRangeMake(
start: CMTime.zero,
duration: CMTimeMakeWithSeconds(Float64(duration), preferredTimescale: framesPerSecond))
exporter.exportAsynchronously(completionHandler: {
//将合并后的视频保存到相册
self.exportDidFinish(session: exporter)
})
}
//将合并后的视频保存到相册
func exportDidFinish(session: AVAssetExportSession) {
print("视频合并成功！")
let outputURL = session.outputURL!
//将录制好的录像保存到照片库中
PHPhotoLibrary.shared().performChanges({
PHAssetChangeRequest.creationRequestForAssetFromVideo(atFileURL: outputURL)
}, completionHandler: { (isSuccess: Bool, error: Error?) in
DispatchQueue.main.async {
//重置参数
self.reset()
//弹出提示框
let alertController = UIAlertController(title: "视频保存成功",
message: "是否需要回看录像？",
preferredStyle: .alert)
let okAction = UIAlertAction(title: "确定", style: .default, handler: {
action in
//录像回看
self.reviewRecord(outputURL: outputURL)
})
let cancelAction = UIAlertAction(title: "取消", style: .cancel,
handler: nil)
alertController.addAction(okAction)
alertController.addAction(cancelAction)
self.present(alertController, animated: true,
completion: nil)
}
})
}
//视频保存成功，重置各个参数，准备新视频录制
func reset() {
//删除视频片段
for assetURL in assetURLs {
if(FileManager.default.fileExists(atPath: assetURL)) {
do {
try FileManager.default.removeItem(atPath: assetURL)
} catch _ {
}
print("删除视频片段: \(assetURL)")
}
}
//进度条还原
let subviews = progressBar.subviews
for subview in subviews {
subview.removeFromSuperview()
}
//各个参数还原
videoAssets.removeAll(keepingCapacity: false)
assetURLs.removeAll(keepingCapacity: false)
appendix = 1
oldX = 0
stopRecording = false
remainingTime = totalSeconds
}
//录像回看
func reviewRecord(outputURL: URL) {
//定义一个视频播放器，通过本地文件路径初始化
let player = AVPlayer(url: outputURL)
let playerViewController = AVPlayerViewController()
playerViewController.player = player
self.present(playerViewController, animated: true) {
playerViewController.player!.play()
}
}
}
附：合并成 mp4 格式的视频
上面样例中，我们是先录制好 mov 格式的视频片段，然后将它们合并成一个完整的 mov 视频。如果想最终生成一个 mp4 文件，只需在合并时修改下输出格式和文件名即可（见下方高亮处）：
//获取合并后的视频路径
let documentsPath = NSSearchPathForDirectoriesInDomains(.documentDirectory,
.userDomainMask,true)[0]
let destinationPath = documentsPath + "/mergeVideo-\(arc4random()%1000).mp4"
print("合并后的视频：\(destinationPath)")
let videoPath = URL(fileURLWithPath: destinationPath as String)
let exporter = AVAssetExportSession(asset: composition,
presetName:AVAssetExportPresetHighestQuality)!
exporter.outputURL = videoPath
exporter.outputFileType = AVFileType.mp4