ios - AVCameraInput - 将相机从前切换到后时崩溃

Question

我正在使用 AV 通过我的应用程序录制视频，并且我有一个按钮可以在相机 View (前置和后置相机)之间切换，默认设置为后置。从后面切换到前面工作得很好。但是，从前面切换到后面会导致应用程序崩溃。

- (IBAction)btnSwapCamerasClicked:(id)sender {

//Change camera source
if(session)
{
    //Indicate that some changes will be made to the session
    [session beginConfiguration];

    //Remove existing input
    AVCaptureInput* currentCameraInput = [session.inputs objectAtIndex:0];
    [session removeInput:currentCameraInput];

    //Get new input
    AVCaptureDevice *newCamera = nil;
    if(((AVCaptureDeviceInput*)currentCameraInput).device.position == AVCaptureDevicePositionBack)
    {
        newCamera = [self cameraWithPosition:AVCaptureDevicePositionFront];
    }
    else
    {
        newCamera = [self cameraWithPosition:AVCaptureDevicePositionBack];
    }

    //Add input to session
    NSError *err = nil;
    AVCaptureDeviceInput *newVideoInput = [[AVCaptureDeviceInput alloc] initWithDevice:newCamera error:&err];
    if(!newVideoInput || err)
    {
        NSLog(@"Error creating capture device input: %@", err.localizedDescription);
    }
    else
    {
          //THIS IS THE SPOT THAT CRASHES.
        [session addInput:newVideoInput];
    }

    //Commit all the configuration changes at once
    [session commitConfiguration];
}

}

崩溃发生在[session addInput:newVideoInput]下；并返回以下错误文本:

2015-03-03 11:25:59.566 The SWAT App Beta[1769:365194] * Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '* Multiple audio/video AVCaptureInputs are not currently supported.' *** First throw call stack: (0x185c002d4 0x1975c80e4 0x1843ad39c 0x1843accd4 0x10004ac14 0x18a818fb4 0x18a80201c 0x18a818950 0x18a8185dc 0x18a811a74 0x18a7e57f0 0x18aa85274 0x18a7e3d04 0x185bb8250 0x185bb74f4 0x185bb55a4 0x185ae1404 0x18f4eb6fc 0x18a84a2b4 0x10004bb70 0x197c6ea08) libc++abi.dylib: terminating with uncaught exception of type NSException

我不完全确定为什么似乎有多个输入，因为在我列出的代码中我删除了旧的输入，并且从后到前工作得很好。不确定为什么从前到后会让应用程序自行终止。

有什么想法吗？

Answer 1

我通过将用于切换相机的代码重写为我专有的代码来解决我的问题。我创建了一个名为 currentCam 的 NSString，我根据当前情况将文本更改为“Back”和“Front”之间。代码如下:

- (IBAction)btnSwapCamerasClicked:(id)sender {

[session beginConfiguration];


if ([currentCam isEqualToString:@"Back"])
{
    NSArray *inputs = [session inputs];

    for (AVCaptureInput *input in inputs)
    {
        [session removeInput:input];
    }

    //Video input
    AVCaptureDevice *newCamera = nil;
    newCamera = [self cameraWithPosition:AVCaptureDevicePositionFront];

    //Audio input
    AVCaptureDevice *audioDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeAudio];
    AVCaptureDeviceInput * audioInput = [AVCaptureDeviceInput deviceInputWithDevice:audioDevice error:nil];


    NSError *err = nil;
    AVCaptureDeviceInput *newVideoInput = [[AVCaptureDeviceInput alloc] initWithDevice:newCamera error:&err];
    if(!newVideoInput || err)
    {
        NSLog(@"Error creating capture device input: %@", err.localizedDescription);
    }
    else
    {

        [session addInput:newVideoInput];
        [session addInput:audioInput];

        newVideoInput = nil;
        audioInput = nil;
        audioDevice = nil;
        newCamera = nil;
        inputs = nil;


    }

    currentCam = @"Front";


}
else if ([currentCam isEqualToString:@"Front"])
{
    NSArray *inputs = [session inputs];

    for (AVCaptureInput *input in inputs)
    {
        [session removeInput:input];
    }

    //Video input
    AVCaptureDevice *newCamera = nil;
    newCamera = [self cameraWithPosition:AVCaptureDevicePositionBack];

    //Audio input
    AVCaptureDevice *audioDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeAudio];
    AVCaptureDeviceInput * audioInput = [AVCaptureDeviceInput deviceInputWithDevice:audioDevice error:nil];


    NSError *err = nil;
    AVCaptureDeviceInput *newVideoInput = [[AVCaptureDeviceInput alloc] initWithDevice:newCamera error:&err];
    if(!newVideoInput || err)
    {
        NSLog(@"Error creating capture device input: %@", err.localizedDescription);
    }
    else
    {

        [session addInput:newVideoInput];
        [session addInput:audioInput];

        newVideoInput = nil;
        audioInput = nil;
        audioDevice = nil;
        newCamera = nil;
        inputs = nil;
    }

    currentCam = @"Back";
}
else
{
    //Camera is some weird third camera that doesn't exist yet! :O
    NSLog(@"wat");
}

[session commitConfiguration];
}