crashing on video capture with AVFoundation

Question

I am trying to implement video capture in my app using AVFoundation. I have the following code under viewDidLoad:

session = [[AVCaptureSession alloc] init];
movieFileOutput = [[AVCaptureMovieFileOutput alloc] init];
videoInputDevice = [[AVCaptureDeviceInput alloc] init];
AVCaptureDevice *videoDevice = [self frontFacingCameraIfAvailable];

if (videoDevice)
{
    NSError *error;

    videoInputDevice = [AVCaptureDeviceInput deviceInputWithDevice:videoDevice error:&error];

    if (!error)
    {
        if ([session canAddInput:videoInputDevice])
            [session addInput:videoInputDevice];
        else 
            NSLog (@"Couldn't add input.");
    }

}


AVCaptureDevice *audioCaptureDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeAudio];
NSError *audioError = nil;
AVCaptureDeviceInput *audioInput = [AVCaptureDeviceInput deviceInputWithDevice:audioCaptureDevice error:&audioError];

if (audioInput)
{
    [session addInput:audioInput];
}

movieFileOutput = [[AVCaptureMovieFileOutput alloc] init];

Float64 TotalSeconds = 35;          //Total seconds
int32_t preferredTimeScale = 30;    //Frames per second
CMTime maxDuration = CMTimeMakeWithSeconds(TotalSeconds, preferredTimeScale);   
movieFileOutput.maxRecordedDuration = maxDuration;

movieFileOutput.minFreeDiskSpaceLimit = 1024 * 1024;                        

if ([session canAddOutput:movieFileOutput])
    [session addOutput:movieFileOutput];

[session setSessionPreset:AVCaptureSessionPresetMedium];
if ([session canSetSessionPreset:AVCaptureSessionPreset640x480])        //Check size based configs are supported before setting them
    [session setSessionPreset:AVCaptureSessionPreset640x480];

[self cameraSetOutputProperties];


[session startRunning];

This code is in the implementation for a button that is to start the capture, among other things:

NSString *outputPath = [[NSString alloc] initWithFormat:@"%@%@", NSTemporaryDirectory(), @"output.mov"];
NSURL *outputURL = [[NSURL alloc] initFileURLWithPath:outputPath];
NSFileManager *fileManager = [NSFileManager defaultManager];
if ([fileManager fileExistsAtPath:outputPath])
{
    NSError *error;
    if ([fileManager removeItemAtPath:outputPath error:&error] == NO)
    {
        //Error - handle if requried
    }
}
[outputPath release];
//Start recording
[movieFileOutput startRecordingToOutputFileURL:outputURL recordingDelegate:self];
[outputURL release];

When I try to run it on a device, it crashes when I try to load the view that all of this is supposed to happen on. Xcode gives me a "Thread 1: EXC_BAD_ACCESS (code=1, address=0x4) at:

AVFoundation`-[AVCaptureDeviceInput _setDevice:]:
(stuff)
0x3793f608:  ldr    r0, [r1, r0]

The error is given at that last line. I assume this has something to do with the AVCaptureDeviceInput somewhere, but I am blanking on what it could be. Does anyone have any idea what I am missing here? Thanks.

Edit: After fiddling with breakpoints, I've figured out that the crash happens at this line:

AVCaptureDevice *videoDevice = [self frontFacingCameraIfAvailable];

So something to do with that method? Here's the implementation file that I have for it, maybe something is wrong there.

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

//  couldn't find one on the front, so just get the default video device.
if ( ! captureDevice)
{
    captureDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
}

return captureDevice;

Edit 2: Could it maybe be that I am using

AVCaptureDevice *videoDevice = [self frontFacingCameraIfAvailable];

and the 'self' is throwing a wrench in it somehow? I know that when creating a CALayer it is possible to do

CALayer *aLayer = [CALayer layer];

but I don't know the AVCaptureDevice equivalent of this, if there is one. I am not sure what else it could be, by all accounts my code seems fine and I've tried cleaning the project, restarting Xcode, restarting the computer, etc.

when you say the last line, what line are you specifically talking about? The last line of code in your post is a release. — Dima
sorry, I meant the last line of the last code block, the 0x3793f608. that's the only place I get any sort of error. — lunadiviner

OFRBG OFRBG · Accepted Answer · 2012-06-26T19:00:51

I'm pretty sure the problem is that you're running the program on the simulator. The simulator can't use those resources.

crashing on video capture with AVFoundation

2 Answers