AVCameraInput - 从前到后切换相机时崩溃答案

【问题标题】：AVCameraInput - crash when switching camera from front to backAVCameraInput - 从前到后切换相机时崩溃
【发布时间】：2015-05-04 09:56:54
【问题描述】：

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，可以在前后摄像头的摄像头视图之间切换，默认为后背。从后到前切换效果很好。但是，从前向后切换会导致应用崩溃。

- (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];我返回以下错误文本：

2015-03-03 11:25:59.566 SWAT App Beta[1769:365194] * 由于未捕获的异常“NSInvalidArgumentException”而终止应用程序，原因：“* 多个音频/视频 AVCaptureInputs 是目前不支持。 *** 首先抛出调用堆栈：（0x185c002d4 0x1975c80e4 0x1843ad39c 0x1843accd4 0x10004ac14 0x18a818fb4 0x18a80201c 0x18a818950 0x18a8185dc 0x18a811a74 0x18a7e57f0 0x18aa85274 0x18a7e3d04 0x185bb8250 0x185bb74f4 0x185bb55a4 0x185ae1404 0x18f4eb6fc 0x18a84a2b4 0x10004bb70 0x197c6ea08） libc++abi.dylib：以 NSException 类型的未捕获异常终止

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，我删除了旧输入，而且它从后到前工作得很好。不知道为什么从前到后会让应用程序自毁。

有什么想法吗？

【问题讨论】：

更新——我想我发现了一些可能导致问题的东西。当我试图从前到后再次检查相机位置时，我的 if 语句不起作用。我重写了 if 以将“else if cam is front”添加到 else 条件和第三个 else，我的代码传递给第三个 else，它不检查任何条件。
更新 2：这让我得到了答案。我使用的解决方案见下文。

标签： ios xcode avfoundation video-capture

【解决方案1】：

我通过将用于切换相机的代码重写为我自己编写的代码解决了我的问题。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];
}

【讨论】：

【解决方案2】：

只有这么多的代码才能工作

- (IBAction)switchCamera:(id)sender {

    [captureSession beginConfiguration];
    NSArray *inputs = [captureSession inputs];

    //Remove all inputs
    for (AVCaptureInput *input in inputs)
    {
        [captureSession removeInput:input];
    }

    //Video input
    AVCaptureDevice *newCamera = nil;
    if ([currentCam isEqualToString:@"Back"]){
        newCamera = [self cameraWithPosition:AVCaptureDevicePositionFront];
           currentCam = @"Front";
    }else{
        newCamera = [self cameraWithPosition:AVCaptureDevicePositionBack];
         currentCam = @"Back";
    }
    //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
    {
        [captureSession addInput:newVideoInput];
        [captureSession addInput:audioInput];
    }
[captureSession commitConfiguration];
}

【讨论】：