iOS开发进阶 - 用AVFoundation自定义视频录制功能

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系统自带的录制视频的功能显然无法满足美工和项目经理的要求，自定义视频录制就非常重要了，那么下面来带大家制作属于自己的视频录制界面。

简介

自定义视频录制需要用到的框架主要是AVFoundation和CoreMedia，包括视频输出，输入和文件的读写，下面给大家罗列一下将要用到的类：

• AVCaptureSession
• AVCaptureVideoPreviewLayer
• AVCaptureDeviceInput
• AVCaptureConnection
• AVCaptureVideoDataOutput
• AVCaptureAudioDataOutput
• AVAssetWriter
• AVAssetWriterInput

下面详细介绍每个类和代码实现

AVCaptureSession

AVCaptureSession是AVFoundation捕捉类的中心枢纽，我们先从这个类入手，在视频捕获时,客户端可以实例化AVCaptureSession并添加适当的AVCaptureInputs、AVCaptureDeviceInput和输出，比如AVCaptureMovieFileOutput。通过[AVCaptureSession startRunning]开始数据流从输入到输出,和[AVCaptureSession stopRunning]停止输出输入的流动。客户端可以通过设置sessionPreset属性定制录制质量水平或输出的比特率。

//捕获视频的会话
- (AVCaptureSession *)recordSession {
    if (_recordSession == nil) {
        _recordSession = [[AVCaptureSession alloc] init];
        //添加后置摄像头的输出
        if ([_recordSession canAddInput:self.backCameraInput]) {
            [_recordSession addInput:self.backCameraInput];
        }
        //添加后置麦克风的输出
        if ([_recordSession canAddInput:self.audioMicInput]) {
            [_recordSession addInput:self.audioMicInput];
        }
        //添加视频输出
        if ([_recordSession canAddOutput:self.videoOutput]) {
            [_recordSession addOutput:self.videoOutput];
            //设置视频的分辨率为后置摄像头
            NSDictionary* actual = self.videoOutput.videoSettings;
            _cx = [[actual objectForKey:@"Height"] integerValue];
            _cy = [[actual objectForKey:@"Width"] integerValue];
        }
        //添加音频输出
        if ([_recordSession canAddOutput:self.audioOutput]) {
            [_recordSession addOutput:self.audioOutput];
        }
        //设置视频录制的方向
        self.videoConnection.videoOrientation = AVCaptureVideoOrientationPortrait;
    }
    return _recordSession;
}

AVCaptureDevice

AVCaptureDevice的每个实例对应一个设备,如摄像头或麦克风。AVCaptureDevice的实例不能直接创建。所有现有设备可以使用类方法devicesWithMediaType:defaultDeviceWithMediaType:获取，设备可以提供一个或多个给定流媒体类型。AVCaptureDevice实例可用于提供给AVCaptureSession创建一个为AVCaptureDeviceInput类型的输入源。

//返回前置摄像头
- (AVCaptureDevice *)frontCamera {
    return [self cameraWithPosition:AVCaptureDevicePositionFront];
}

//返回后置摄像头
- (AVCaptureDevice *)backCamera {
    return [self cameraWithPosition:AVCaptureDevicePositionBack];
}

//用来返回是前置摄像头还是后置摄像头
- (AVCaptureDevice *)cameraWithPosition:(AVCaptureDevicePosition) position {
    //返回和视频录制相关的所有默认设备
    NSArray *devices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
    //遍历这些设备返回跟position相关的设备
    for (AVCaptureDevice *device in devices) {
        if ([device position] == position) {
            return device;
        }
    }
    return nil;
}
//开启闪光灯
- (void)openFlashLight {
    AVCaptureDevice *backCamera = [self backCamera];
    if (backCamera.torchMode == AVCaptureTorchModeOff) {
        [backCamera lockForConfiguration:nil];
        backCamera.torchMode = AVCaptureTorchModeOn;
        backCamera.flashMode = AVCaptureFlashModeOn;
        [backCamera unlockForConfiguration];
    }
}
//关闭闪光灯
- (void)closeFlashLight {
    AVCaptureDevice *backCamera = [self backCamera];
    if (backCamera.torchMode == AVCaptureTorchModeOn) {
        [backCamera lockForConfiguration:nil];
        backCamera.torchMode = AVCaptureTorchModeOff;
        backCamera.flashMode = AVCaptureTorchModeOff;
        [backCamera unlockForConfiguration];
    }
}

AVCaptureDeviceInput

AVCaptureDeviceInput 是AVCaptureSession输入源,提供媒体数据从设备连接到系统，通过AVCaptureDevice的实例化得到，就是我们将要用到的设备输出源设备，也就是前后摄像头，通过[AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo]方法获得。

//后置摄像头输入
- (AVCaptureDeviceInput *)backCameraInput {
    if (_backCameraInput == nil) {
        NSError *error;
        _backCameraInput = [[AVCaptureDeviceInput alloc] initWithDevice:[self backCamera] error:&error];
        if (error) {
            [SVProgressHUD showErrorWithStatus:@"获取后置摄像头失败~"];
        }
    }
    return _backCameraInput;
}

//前置摄像头输入
- (AVCaptureDeviceInput *)frontCameraInput {
    if (_frontCameraInput == nil) {
        NSError *error;
        _frontCameraInput = [[AVCaptureDeviceInput alloc] initWithDevice:[self frontCamera] error:&error];
        if (error) {
            [SVProgressHUD showErrorWithStatus:@"获取前置摄像头失败~"];
        }
    }
    return _frontCameraInput;
}

AVCaptureVideoPreviewLayer

是CoreAnimation里面layer的一个子类，用来做为AVCaptureSession预览视频输出，简单来说就是来做为拍摄的视频呈现的一个layer。

//捕获到的视频呈现的layer
- (AVCaptureVideoPreviewLayer *)previewLayer {
    if (_previewLayer == nil) {
        //通过AVCaptureSession初始化
        AVCaptureVideoPreviewLayer *preview = [[AVCaptureVideoPreviewLayer alloc] initWithSession:self.recordSession];
        //设置比例为铺满全屏
        preview.videoGravity = AVLayerVideoGravityResizeAspectFill;
        _previewLayer = preview;
    }
    return _previewLayer;
}

AVCaptureMovieFileOutput

AVCaptureMovieFileOutput是AVCaptureFileOutput的子类，用来写入QuickTime视频类型的媒体文件。因为这个类在iphone上并不能实现暂停录制，和不能定义视频文件的类型，所以在这里并不使用，而是用灵活性更强的AVCaptureVideoDataOutput和AVCaptureAudioDataOutput来实现视频的录制。

AVCaptureVideoDataOutput

AVCaptureVideoDataOutput是AVCaptureOutput一个子类，可以用于用来输出未压缩或压缩的视频捕获的帧，AVCaptureVideoDataOutput产生的实例可以使用其他媒体视频帧适合的api处理，应用程序可以用captureOutput:didOutputSampleBuffer:fromConnection:代理方法来获取帧数据。

//视频输出
- (AVCaptureVideoDataOutput *)videoOutput {
    if (_videoOutput == nil) {
        _videoOutput = [[AVCaptureVideoDataOutput alloc] init];
        [_videoOutput setSampleBufferDelegate:self queue:self.captureQueue];
        NSDictionary* setcapSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                                        [NSNumber numberWithInt:kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange], kCVPixelBufferPixelFormatTypeKey,
                                        nil];
        _videoOutput.videoSettings = setcapSettings;
    }
    return _videoOutput;
}

AVCaptureAudioDataOutput

AVCaptureAudioDataOutput是AVCaptureOutput的子类，可用于用来输出捕获来的非压缩或压缩的音频样本，AVCaptureAudioDataOutput产生的实例可以使用其他媒体视频帧适合的api处理，应用程序可以用captureOutput:didOutputSampleBuffer:fromConnection:代理方法来获取音频数据。

//音频输出
- (AVCaptureAudioDataOutput *)audioOutput {
    if (_audioOutput == nil) {
        _audioOutput = [[AVCaptureAudioDataOutput alloc] init];
        [_audioOutput setSampleBufferDelegate:self queue:self.captureQueue];
    }
    return _audioOutput;
}

AVCaptureConnection

AVCaptureConnection代表AVCaptureInputPort或端口之间的连接，和一个AVCaptureOutput或AVCaptureVideoPreviewLayer在AVCaptureSession中的呈现。

//视频连接
- (AVCaptureConnection *)videoConnection {
    _videoConnection = [self.videoOutput connectionWithMediaType:AVMediaTypeVideo];
    return _videoConnection;
}

//音频连接
- (AVCaptureConnection *)audioConnection {
    if (_audioConnection == nil) {
        _audioConnection = [self.audioOutput connectionWithMediaType:AVMediaTypeAudio];
    }
    return _audioConnection;
}

AVAssetWriter

AVAssetWriter为写入媒体数据到一个新的文件提供服务，AVAssetWriter的实例可以规定写入媒体文件的格式，如QuickTime电影文件格式或MPEG-4文件格式等等。AVAssetWriter有多个并行的轨道媒体数据，基本的有视频轨道和音频轨道，将会在下面介绍。AVAssetWriter的单个实例可用于一次写入一个单一的文件。那些希望写入多次文件的客户端必须每一次用一个新的AVAssetWriter实例。

//初始化方法
- (instancetype)initPath:(NSString*)path Height:(NSInteger)cy width:(NSInteger)cx channels:(int)ch samples:(Float64) rate {
    self = [super init];
    if (self) {
        self.path = path;
        //先把路径下的文件给删除掉，保证录制的文件是最新的
        [[NSFileManager defaultManager] removeItemAtPath:self.path error:nil];
        NSURL* url = [NSURL fileURLWithPath:self.path];
        //初始化写入媒体类型为MP4类型
        _writer = [AVAssetWriter assetWriterWithURL:url fileType:AVFileTypeMPEG4 error:nil];
        //使其更适合在网络上播放
        _writer.shouldOptimizeForNetworkUse = YES;
        //初始化视频输出
        [self initVideoInputHeight:cy width:cx];
        //确保采集到rate和ch
        if (rate != 0 && ch != 0) {
            //初始化音频输出
            [self initAudioInputChannels:ch samples:rate];
        }
    }
    return self;
}

AVAssetWriterInput

用AVAssetWriterInput去拼接一个多媒体样本类型为CMSampleBuffer的实例到AVAssetWriter对象的输出文件的一个轨道；当有多个输入时， AVAssetWriter试图在用于存储和播放效率的理想模式写媒体数据。它的每一个输入信号，是否能接受媒体的数据根据通过readyForMoreMediaData的值来判断。如果readyForMoreMediaData是YES ，说明输入可以接受媒体数据。并且你只能媒体数据追加到输入端。

//初始化视频输入
- (void)initVideoInputHeight:(NSInteger)cy width:(NSInteger)cx {
    //录制视频的一些配置，分辨率，编码方式等等
    NSDictionary* settings = [NSDictionary dictionaryWithObjectsAndKeys:
                              AVVideoCodecH264, AVVideoCodecKey,
                              [NSNumber numberWithInteger: cx], AVVideoWidthKey,
                              [NSNumber numberWithInteger: cy], AVVideoHeightKey,
                              nil];
    //初始化视频写入类
    _videoInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo outputSettings:settings];
    //表明输入是否应该调整其处理为实时数据源的数据
    _videoInput.expectsMediaDataInRealTime = YES;
    //将视频输入源加入
    [_writer addInput:_videoInput];
}

//初始化音频输入
- (void)initAudioInputChannels:(int)ch samples:(Float64)rate {
    //音频的一些配置包括音频各种这里为AAC,音频通道、采样率和音频的比特率
    NSDictionary *settings = [NSDictionary dictionaryWithObjectsAndKeys:
                              [ NSNumber numberWithInt: kAudioFormatMPEG4AAC], AVFormatIDKey,
                              [ NSNumber numberWithInt: ch], AVNumberOfChannelsKey,
                              [ NSNumber numberWithFloat: rate], AVSampleRateKey,
                              [ NSNumber numberWithInt: 128000], AVEncoderBitRateKey,
                              nil];
    //初始化音频写入类
    _audioInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeAudio outputSettings:settings];
    //表明输入是否应该调整其处理为实时数据源的数据
    _audioInput.expectsMediaDataInRealTime = YES;
    //将音频输入源加入
    [_writer addInput:_audioInput];

}

---

上面是录制之前的一些需要的类和配置，下面介绍的是如何将获取到的数据呈现出来和怎样进行文件写入

写入数据

#pragma mark - 写入数据
- (void) captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection {
    BOOL isVideo = YES;
    @synchronized(self) {
        if (!self.isCapturing  || self.isPaused) {
            return;
        }
        if (captureOutput != self.videoOutput) {
            isVideo = NO;
        }

        //初始化编码器，当有音频和视频参数时创建编码器
        if ((self.recordEncoder == nil) && !isVideo)                     
        {  
            CMFormatDescriptionRef fmt = CMSampleBufferGetFormatDescription(sampleBuffer);
            [self setAudioFormat:fmt];
            NSString *videoName = [NSString getUploadFile_type:@"video" fileType:@"mp4"];
            self.videoPath = [[self getVideoCachePath] stringByAppendingPathComponent:videoName];
            self.recordEncoder = [WCLRecordEncoder encoderForPath:self.videoPath Height:_cy width:_cx channels:_channels samples:_samplerate];
        }

        //判断是否中断录制过
        if (self.discont) {
            if (isVideo) {
                return;
            }
            self.discont = NO;
            // 计算暂停的时间
            CMTime pts = CMSampleBufferGetPresentationTimeStamp(sampleBuffer);
            CMTime last = isVideo ? _lastVideo : _lastAudio;
            if (last.flags & kCMTimeFlags_Valid) {
                if (_timeOffset.flags & kCMTimeFlags_Valid) {
                    pts = CMTimeSubtract(pts, _timeOffset);
                }
                CMTime offset = CMTimeSubtract(pts, last);
                if (_timeOffset.value == 0) {
                    _timeOffset = offset;
                }else {
                    _timeOffset = CMTimeAdd(_timeOffset, offset);
                }
            }
            _lastVideo.flags = 0;
            _lastAudio.flags = 0;
        }
        // 增加sampleBuffer的引用计时,这样我们可以释放这个或修改这个数据，防止在修改时被释放
        CFRetain(sampleBuffer);
        if (_timeOffset.value > 0) {
            CFRelease(sampleBuffer);
            //根据得到的timeOffset调整
            sampleBuffer = [self adjustTime:sampleBuffer by:_timeOffset];
        }
        // 记录暂停上一次录制的时间
        CMTime pts = CMSampleBufferGetPresentationTimeStamp(sampleBuffer);
        CMTime dur = CMSampleBufferGetDuration(sampleBuffer);
        if (dur.value > 0) {
            pts = CMTimeAdd(pts, dur);
        }
        if (isVideo) {
            _lastVideo = pts;
        }else {
            _lastAudio = pts;
        }
    }
    CMTime dur = CMSampleBufferGetPresentationTimeStamp(sampleBuffer);
    if (self.startTime.value == 0) {
        self.startTime = dur;
    }
    CMTime sub = CMTimeSubtract(dur, self.startTime);
    self.currentRecordTime = CMTimeGetSeconds(sub);
    if (self.currentRecordTime > self.maxRecordTime) {
        if (self.currentRecordTime - self.maxRecordTime < 0.1) {
            if ([self.delegate respondsToSelector:@selector(recordProgress:)]) {
                dispatch_async(dispatch_get_main_queue(), ^{
                    [self.delegate recordProgress:self.currentRecordTime/self.maxRecordTime];
                });
            }
        }
        return;
    }
    if ([self.delegate respondsToSelector:@selector(recordProgress:)]) {
        dispatch_async(dispatch_get_main_queue(), ^{
            [self.delegate recordProgress:self.currentRecordTime/self.maxRecordTime];
        });
    }
    // 进行数据编码
    [self.recordEncoder encodeFrame:sampleBuffer isVideo:isVideo];
    CFRelease(sampleBuffer);
}

//设置音频格式
- (void)setAudioFormat:(CMFormatDescriptionRef)fmt {
    const AudioStreamBasicDescription *asbd = CMAudioFormatDescriptionGetStreamBasicDescription(fmt);
    _samplerate = asbd->mSampleRate;
    _channels = asbd->mChannelsPerFrame;

}

//调整媒体数据的时间
- (CMSampleBufferRef)adjustTime:(CMSampleBufferRef)sample by:(CMTime)offset {
    CMItemCount count;
    CMSampleBufferGetSampleTimingInfoArray(sample, 0, nil, &count);
    CMSampleTimingInfo* pInfo = malloc(sizeof(CMSampleTimingInfo) * count);
    CMSampleBufferGetSampleTimingInfoArray(sample, count, pInfo, &count);
    for (CMItemCount i = 0; i < count; i++) {
        pInfo[i].decodeTimeStamp = CMTimeSubtract(pInfo[i].decodeTimeStamp, offset);
        pInfo[i].presentationTimeStamp = CMTimeSubtract(pInfo[i].presentationTimeStamp, offset);
    }
    CMSampleBufferRef sout;
    CMSampleBufferCreateCopyWithNewTiming(nil, sample, count, pInfo, &sout);
    free(pInfo);
    return sout;
}

//通过这个方法写入数据
- (BOOL)encodeFrame:(CMSampleBufferRef) sampleBuffer isVideo:(BOOL)isVideo {
    //数据是否准备写入
    if (CMSampleBufferDataIsReady(sampleBuffer)) {
        //写入状态为未知,保证视频先写入
        if (_writer.status == AVAssetWriterStatusUnknown && isVideo) {
            //获取开始写入的CMTime
            CMTime startTime = CMSampleBufferGetPresentationTimeStamp(sampleBuffer);
            //开始写入
            [_writer startWriting];
            [_writer startSessionAtSourceTime:startTime];
        }
        //写入失败
        if (_writer.status == AVAssetWriterStatusFailed) {
            NSLog(@"writer error %@", _writer.error.localizedDescription);
            return NO;
        }
        //判断是否是视频
        if (isVideo) {
            //视频输入是否准备接受更多的媒体数据
            if (_videoInput.readyForMoreMediaData == YES) {
                //拼接数据
                [_videoInput appendSampleBuffer:sampleBuffer];
                return YES;
            }
        }else {
            //音频输入是否准备接受更多的媒体数据
            if (_audioInput.readyForMoreMediaData) {
                //拼接数据
                [_audioInput appendSampleBuffer:sampleBuffer];
                return YES;
            }
        }
    }
    return NO;
}

完成录制并写入相册

//停止录制
- (void) stopCaptureHandler:(void (^)(UIImage *movieImage))handler {
    @synchronized(self) {
        if (self.isCapturing) {
            NSString* path = self.recordEncoder.path;
            NSURL* url = [NSURL fileURLWithPath:path];
            self.isCapturing = NO;
            dispatch_async(_captureQueue, ^{
                [self.recordEncoder finishWithCompletionHandler:^{
                    self.isCapturing = NO;
                    self.recordEncoder = nil;
                    [[PHPhotoLibrary sharedPhotoLibrary] performChanges:^{
                        [PHAssetChangeRequest creationRequestForAssetFromVideoAtFileURL:url];
                    } completionHandler:^(BOOL success, NSError * _Nullable error) {
                        NSLog(@"保存成功");
                    }];
                    [self movieToImageHandler:handler];
                }];
            });
        }
    }
}

//获取视频第一帧的图片
- (void)movieToImageHandler:(void (^)(UIImage *movieImage))handler {
    NSURL *url = [NSURL fileURLWithPath:self.videoPath];
    AVURLAsset *asset = [[AVURLAsset alloc] initWithURL:url options:nil];
    AVAssetImageGenerator *generator = [[AVAssetImageGenerator alloc] initWithAsset:asset];
    generator.appliesPreferredTrackTransform = TRUE;
    CMTime thumbTime = CMTimeMakeWithSeconds(0, 60);
    generator.apertureMode = AVAssetImageGeneratorApertureModeEncodedPixels;
    AVAssetImageGeneratorCompletionHandler generatorHandler =
    ^(CMTime requestedTime, CGImageRef im, CMTime actualTime, AVAssetImageGeneratorResult result, NSError *error){
        if (result == AVAssetImageGeneratorSucceeded) {
            UIImage *thumbImg = [UIImage imageWithCGImage:im];
            if (handler) {
                dispatch_async(dispatch_get_main_queue(), ^{
                    handler(thumbImg);
                });
            }
        }
    };
    [generator generateCGImagesAsynchronouslyForTimes:
     [NSArray arrayWithObject:[NSValue valueWithCMTime:thumbTime]] completionHandler:generatorHandler];
}

//完成视频录制时调用
- (void)finishWithCompletionHandler:(void (^)(void))handler {
    [_writer finishWritingWithCompletionHandler: handler];
}

---

以上就是本博客内容的全部内容，大家如果有什么疑问可以问我，本文附带有demo，大家可以去看看具体怎么使用，有用的话可以点一下star，谢谢大家的阅读~~

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