self.startRunning doesn't function properly

Question

I'm currently creating an iOS application that uses the camera to capture 15 frames per second for 30 seconds (a total of 450 frames). The problem is that [self.session startRunning] (the last line of the code provided) doesn't seem to be working; I say this because I've set up an array called hues to take the average red values of each of the 450 frames that should be captured. However, even after starting and stopping detection, the array remains empty. What am I missing?

#import "ViewController.h"
#import <AVFoundation/AVFoundation.h>

@interface ViewController ()

@property (nonatomic, strong) AVCaptureSession *session;
@property (nonatomic, strong) NSMutableArray *hues;

@end

const int SECONDS = 15;
const int FPS = 30;

@implementation ViewController

- (void)viewDidLoad
{
[super viewDidLoad];

self.hues = [[NSMutableArray alloc] init]; // initiate things (from old code)
self.session = [[AVCaptureSession alloc] init];
self.session.sessionPreset = AVCaptureSessionPresetLow;

NSInteger numberOfFramesCaptured = self.hues.count;

// initialize the session with proper settings (from docs)

NSError *error = nil;

AVCaptureDevice *captureDevice; // initialize captureDevice and input, and add input (from old code)
AVCaptureDeviceInput *videoInput = [[AVCaptureDeviceInput alloc] initWithDevice:captureDevice error:&error];
if ([self.session canAddInput:videoInput])
{ // fails
    [self.session addInput:videoInput];
}

// find the max fps we can get from the given device (from old code)
AVCaptureDeviceFormat *currentFormat = [captureDevice activeFormat];

for (AVCaptureDeviceFormat *format in captureDevice.formats) // executes twice
{ // skips all of this
    NSArray *ranges = format.videoSupportedFrameRateRanges;
    AVFrameRateRange *frameRates = ranges[0];

    // find the lowest resolution format at the frame rate we want (from old code)
    if (frameRates.maxFrameRate == FPS && (!currentFormat || (CMVideoFormatDescriptionGetDimensions(format.formatDescription).width < CMVideoFormatDescriptionGetDimensions(currentFormat.formatDescription).width && CMVideoFormatDescriptionGetDimensions(format.formatDescription).height < CMVideoFormatDescriptionGetDimensions(currentFormat.formatDescription).height)))
    {
        currentFormat = format;
    }
}

// tell the device to use the max frame rate (from old code)
[captureDevice lockForConfiguration:nil];
captureDevice.torchMode = AVCaptureTorchModeOn;
captureDevice.activeFormat = currentFormat;
captureDevice.activeVideoMinFrameDuration = CMTimeMake(1, FPS);
captureDevice.activeVideoMaxFrameDuration = CMTimeMake(1, FPS);
[captureDevice unlockForConfiguration];

// set the output (from old code)
AVCaptureVideoDataOutput *videoOutput = [[AVCaptureVideoDataOutput alloc] init];

// create a queue to run the capture on (from old code)
dispatch_queue_t queue = dispatch_queue_create("queue", NULL);

// setup our delegate (from old code)
[videoOutput setSampleBufferDelegate:self queue:queue];

// configure the pixel format (from old code)
videoOutput.videoSettings = [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithUnsignedInt:kCVPixelFormatType_32BGRA], (id)kCVPixelBufferPixelFormatTypeKey, nil];
videoOutput.alwaysDiscardsLateVideoFrames = NO;

[self.session addOutput:videoOutput];

// start the video session
[self.session startRunning]; // PROBLEM OCCURS HERE

Answer 1

In your code AVCaptureDevice *captureDevice; never initialized.