Iphone 录制视频时更改相机捕获设备

我正在开发一个iPhone应用程序。在这种情况下，需要暂停和恢复相机。因此，我使用了

AVFoundation

，而不是使用

UIImagePickerController

我的代码是：

 - (void) startup :(BOOL)isFrontCamera
    {

        if (_session == nil)
        {
            NSLog(@"Starting up server");

            self.isCapturing = NO;
            self.isPaused = NO;
            _currentFile = 0;
            _discont = NO;

            // create capture device with video input
            _session = [[AVCaptureSession alloc] init];
            AVCaptureDevice *cameraDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];

        if(isFrontCamera)
        {
            NSArray *videoDevices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
            AVCaptureDevice *captureDevice = nil;
            for (AVCaptureDevice *device in videoDevices)
            {
                if (device.position == AVCaptureDevicePositionFront)
                {
                    captureDevice = device;
                    break;  
                }  
            }

            cameraDevice = captureDevice;

        }


            cameraDevice=[AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
    AVCaptureDeviceInput* input = [AVCaptureDeviceInput deviceInputWithDevice:cameraDevice error:nil];

            [_session addInput:input];

            // audio input from default mic
            AVCaptureDevice* mic = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeAudio];
            AVCaptureDeviceInput* micinput = [AVCaptureDeviceInput deviceInputWithDevice:mic error:nil];
            [_session addInput:micinput];

            // create an output for YUV output with self as delegate
            _captureQueue = dispatch_queue_create("uk.co.gdcl.cameraengine.capture", DISPATCH_QUEUE_SERIAL);
            AVCaptureVideoDataOutput* videoout = [[AVCaptureVideoDataOutput alloc] init];
            [videoout setSampleBufferDelegate:self queue:_captureQueue];
            NSDictionary* setcapSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                                            [NSNumber numberWithInt:kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange], kCVPixelBufferPixelFormatTypeKey,
                                            nil];
            videoout.videoSettings = setcapSettings;
            [_session addOutput:videoout];
            _videoConnection = [videoout connectionWithMediaType:AVMediaTypeVideo];

            [_videoConnection setVideoOrientation:AVCaptureVideoOrientationPortrait];

            NSDictionary* actual = videoout.videoSettings;
            _cy = [[actual objectForKey:@"Width"] integerValue];
            _cx = [[actual objectForKey:@"Height"] integerValue];
     AVCaptureAudioDataOutput* audioout = [[AVCaptureAudioDataOutput alloc] init];
            [audioout setSampleBufferDelegate:self queue:_captureQueue];
            [_session addOutput:audioout];
            _audioConnection = [audioout connectionWithMediaType:AVMediaTypeAudio];
     [_session startRunning];

            _preview = [AVCaptureVideoPreviewLayer layerWithSession:_session];
            _preview.videoGravity = AVLayerVideoGravityResizeAspectFill;
        }
    }

在这里，我面临的问题，当我改变相机的前面。当我调用上面的方法，将相机更改为“前”时，预览层被卡住，没有预览。我的疑问是“我们能在捕获会话中间改变捕获设备吗？”请指导我哪里出了问题（或）建议我在录音时如何在前后摄像头之间导航

---

提前谢谢

您不能在会话中期更改captureDevice。一次只能运行一个捕获会话。您可以结束当前会话并创建一个新会话。将有一个轻微的延迟（可能是一秒或两秒，取决于您的cpu负载）

---

我希望苹果能允许多个会话或者每个会话至少有多台设备。。。但是他们没有。。。但是。

您是否考虑过进行多个会话，然后再处理视频文件，将它们合并为一个会话

是的，你可以。你只需要满足一些事情

需要使用AVCaptureVideoDataOutput及其委托进行录制。

在添加新设备输入之前，请确保删除以前的设备输入。

您还必须删除并重新创建AVCaptureVideoDataOutput

我现在正在为它使用这两个函数，它在会话运行时工作

- (void)configureVideoWithDevice:(AVCaptureDevice *)camera {

    [_session beginConfiguration];
    [_session removeInput:_videoInputDevice];
    _videoInputDevice = nil;

    _videoInputDevice = [AVCaptureDeviceInput deviceInputWithDevice:camera error:nil];
    if ([_session canAddInput:_videoInputDevice]) {
        [_session addInput:_videoInputDevice];
    }

    [_session removeOutput:_videoDataOutput];
    _videoDataOutput = nil;

    _videoDataOutput = [[AVCaptureVideoDataOutput alloc] init];
    [_videoDataOutput setSampleBufferDelegate:self queue:_outputQueueVideo];
    NSDictionary* setcapSettings = [NSDictionary dictionaryWithObjectsAndKeys: [NSNumber numberWithInt:kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange], kCVPixelBufferPixelFormatTypeKey, nil];

    _videoDataOutput.videoSettings = setcapSettings;
    [_session addOutput:_videoDataOutput];
    _videoConnection = [_videoDataOutput connectionWithMediaType:AVMediaTypeVideo];

    if([_videoConnection isVideoOrientationSupported]) {
        [_videoConnection setVideoOrientation:AVCaptureVideoOrientationLandscapeRight];
    }  

    [_session commitConfiguration];
}

- (void)configureAudioWithDevice:(AVCaptureDevice *)microphone {
    [_session beginConfiguration];
    _audioInputDevice = [AVCaptureDeviceInput deviceInputWithDevice:microphone error:nil];
    if ([_session canAddInput:_audioInputDevice]) {
        [_session addInput:_audioInputDevice];
    }

    [_session removeOutput:_audioDataOutput];
    _audioDataOutput = nil;

    _audioDataOutput = [[AVCaptureAudioDataOutput alloc] init];
    [_audioDataOutput setSampleBufferDelegate:self queue:_outputQueueAudio];
    [_session addOutput:_audioDataOutput];
    _audioConnection = [_audioDataOutput connectionWithMediaType:AVMediaTypeAudio];

    [_session commitConfiguration];
}

---

这个算法是致命的，我唯一的问题是视频和音频不同步。是否需要同时配置音频和视频？@HighFlyingFantasy肯定有办法。这有点复杂。您必须手动操作音频采样缓冲区的定时信息以匹配视频。因为我们正在重新创建音频输出，它的计时信息每次都将从零开始。您必须跟踪录制音频的时间，并在将其写入文件之前按该值调整audioSampleBuffer。Geraint Davies通过暂停和恢复视频的示例实现了这项技术。两者的混合应该对你有用@hatebyte你能解决音频同步的问题吗？非常感谢