前言
最近在开发一个小项目，要用到 AVFoundation 来录制小视频，在开发的过程中遇到不少的坑，希望记录下来。
整个 AVFoundation 框架真是相当复杂而有序的（这里不得不佩服 Apple 的工程师），要使用 AVFoundation 录制小视频，并且保存成文件，你需要用到以下的类。
- AVCaptureSession
- AVCaptureDeviceInput
- AVCaptureVideoDataOutput
- AVCaptureAudioDataOutput
- AVCaptureConnection
- AVAssetWriter
- AVAssetWriterInput
类的定义
建立一个 Session 类，先定义好必须的属性
class VideoSessionEntity: NSObject {
let session = AVCaptureSession()
var tmpFileURL: NSURL?
var videoInput: AVCaptureDeviceInput?
var videoOutput: AVCaptureVideoDataOutput = AVCaptureVideoDataOutput()
var videoConnection: AVCaptureConnection?
var audioInput: AVCaptureDeviceInput?
var audioOutput: AVCaptureAudioDataOutput = AVCaptureAudioDataOutput()
var audioConnection: AVCaptureConnection?
var assetWriter: AVAssetWriter?
var videoWriterInput: AVAssetWriterInput?
var audioWriterInput: AVAssetWriterInput?
}
我们需要这么多的属性去完成我们的工作，这里面包括视频、音频的相关属性。
- session 是整个录制工作的控制中心
- videoInput 是视频源的入口
- videoOutput 是视频源的出口
- videoConnection 是视频源的控制中心
- audioInput 是音频源的入口
- audioOutput 是音频源的出口
- audioConnection 是音频源的控制中心
创建回调
其中 videoOutput 和 audioOutput 是需要设置 delegate 的，并且，他们的 delegate 方法是同一个的，它们各需要一个 dispatch_queue_t 进行 GCD 异步回调，这样子创建就可以。
let videoDataOutputQueue = dispatch_queue_create("com.firefly.videoDataOutputQueue", DISPATCH_QUEUE_SERIAL)
let audioDataOutputQueue = dispatch_queue_create("com.firefly.audioDataOutputQueue", DISPATCH_QUEUE_SERIAL)
初始化
在初始化这些属性前，先写两个方法，获取设备。
func deviceForVideo() -> AVCaptureDevice? {
let devices = AVCaptureDevice.devicesWithMediaType(AVMediaTypeVideo)
for device in devices {
if let device = device as? AVCaptureDevice {
if device.position == self.videoSource { //在这里选择前后摄像头
return device
}
}
}
return nil
}
func deviceForAudio() -> AVCaptureDevice? {
let devices = AVCaptureDevice.devicesWithMediaType(AVMediaTypeAudio)
for device in devices {
if let device = device as? AVCaptureDevice {
return device
}
}
return nil
}
然后，我们可以初始化这些属性了，其实都是简单的操作，就是比较繁琐。
func configureVideo() {
if let device = FireFlyCore.sharedCore.post.videoManager.deviceForVideo() {
do {
try! device.lockForConfiguration()
device.activeVideoMaxFrameDuration = CMTimeMake(1, 24)
device.unlockForConfiguration()
}
do {
videoInput = try AVCaptureDeviceInput(device: device)
videoOutput.setSampleBufferDelegate(self, queue: videoDataOutputQueue)
if session.canAddInput(videoInput) {
session.addInput(videoInput)
}
if session.canAddOutput(videoOutput) {
session.addOutput(videoOutput)
}
if session.canSetSessionPreset(AVCaptureSessionPreset352x288) {
session.sessionPreset = AVCaptureSessionPreset352x288
}
videoConnection = videoOutput.connectionWithMediaType(AVMediaTypeVideo)
}
catch _ {
}
}
}
func configureAudio() {
if let device = FireFlyCore.sharedCore.post.videoManager.deviceForAudio() {
do {
audioInput = try AVCaptureDeviceInput(device: device)
audioOutput.setSampleBufferDelegate(self, queue: audioDataOutputQueue)
if session.canAddInput(audioInput) {
session.addInput(audioInput)
}
if session.canAddOutput(audioOutput) {
session.addOutput(audioOutput)
}
audioConnection = audioOutput.connectionWithMediaType(AVMediaTypeAudio)
}
catch _ {
}
}
}
如果没有任何问题，你可以调用 session.startRuning() 方法，这个时候，func captureOutput(captureOutput: AVCaptureOutput!, didOutputSampleBuffer sampleBuffer: CMSampleBuffer!, fromConnection connection: AVCaptureConnection!) 代理方法应该可以收到好多的数据回调， 这代表工作正常。
写入文件
我们需要初始化 AssetWriter，初始化 AssetWriter 需要一些参数，它们代表视频、音频的压缩参数。
let videoSetting: [String : AnyObject] = [
AVVideoCodecKey: AVVideoCodecH264,
AVVideoWidthKey: 320,
AVVideoHeightKey: 240,
AVVideoCompressionPropertiesKey: [
AVVideoPixelAspectRatioKey: [
AVVideoPixelAspectRatioHorizontalSpacingKey: 1,
AVVideoPixelAspectRatioVerticalSpacingKey: 1
],
AVVideoMaxKeyFrameIntervalKey: 1,
AVVideoAverageBitRateKey: 1280000
]
]
let audioSetting: [String: AnyObject] = [
AVFormatIDKey: NSNumber(unsignedInt: kAudioFormatMPEG4AAC),
AVNumberOfChannelsKey: 1,
AVSampleRateKey: 22050
]
然后开始初始化 AssetWriter。
- 注意，这里只是初始化，不要在这里调用
startWriting()方法，如果在这此处调用这个方法，你就没有办法设置 startSessionAtSourceTime() 了。 - 这里还有一个坑，
.expectsMediaDataInRealTime = true必须设为 true，否则，视频会丢帧。
func startRecording() {
tmpFileURL = NSURL.fileURLWithPath("\(NSTemporaryDirectory())tmp\(arc4random()).mp4")
do {
assetWriter = try AVAssetWriter(URL: tmpFileURL!, fileType: AVFileTypeMPEG4)
videoWriterInput = AVAssetWriterInput(mediaType: AVMediaTypeVideo, outputSettings: videoSetting)
videoWriterInput?.expectsMediaDataInRealTime = true
videoWriterInput?.transform = CGAffineTransformMakeRotation(CGFloat(M_PI / 2))
if assetWriter!.canAddInput(videoWriterInput!) {
assetWriter!.addInput(videoWriterInput!)
}
audioWriterInput = AVAssetWriterInput(mediaType: AVMediaTypeAudio, outputSettings: audioSetting)
audioWriterInput?.expectsMediaDataInRealTime = true
if assetWriter!.canAddInput(audioWriterInput!) {
assetWriter!.addInput(audioWriterInput!)
}
}
catch _ {
}
}
func endRecording() {
if let assetWriter = assetWriter {
if let videoWriterInput = videoWriterInput {
videoWriterInput.markAsFinished()
}
if let audioWriterInput = audioWriterInput {
audioWriterInput.markAsFinished()
}
assetWriter.finishWritingWithCompletionHandler({ () -> Void in
})
}
}
写入文件
回调方法的可以参考这样的写法，如果需要为视频添加滤镜可以在这里实现。
func captureOutput(captureOutput: AVCaptureOutput!, didOutputSampleBuffer sampleBuffer: CMSampleBuffer!, fromConnection connection: AVCaptureConnection!) {
objc_sync_enter(self)
if let assetWriter = assetWriter {
if assetWriter.status != .Writing && assetWriter.status != .Unknown {
return
}
}
if let assetWriter = assetWriter where assetWriter.status == AVAssetWriterStatus.Unknown {
assetWriter.startWriting()
assetWriter.startSessionAtSourceTime(CMSampleBufferGetPresentationTimeStamp(sampleBuffer))
}
if connection == self.videoConnection {
dispatch_async(videoDataOutputQueue, { () -> Void in
if let videoWriterInput = self.videoWriterInput where videoWriterInput.readyForMoreMediaData {
videoWriterInput.appendSampleBuffer(sampleBuffer)
}
})
}
else if connection == self.audioConnection {
dispatch_async(audioDataOutputQueue, { () -> Void in
if let audioWriterInput = self.audioWriterInput where audioWriterInput.readyForMoreMediaData {
audioWriterInput.appendSampleBuffer(sampleBuffer)
}
})
}
objc_sync_exit(self)
}