A sub-class of AVCaptureSession that adds a few helper properties for simplifying access to device hardware and add capabilities like flipping between the front and back camera.

SimpleCaptureSession.h

//
// SimpleCaptureSession.h
//
// Copyright (c) 2013 Erik Ralston
//
// MIT License
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
//

#import <AVFoundation/AVFoundation.h>

///
/// A class that adds several helpers to AVCapture session to make video recording and camera management easier
///
@interface SimpleCaptureSession : AVCaptureSession

// Devices
@property (nonatomic, readonly) AVCaptureDevice *rearCameraDevice;
@property (nonatomic, readonly) AVCaptureDevice *frontCameraDevice;
@property (nonatomic, readonly) AVCaptureDevice *audioDevice;

// Helpers
- (BOOL)isFrontCameraSupported;

// Methods for safely adding devices (and logging when things go wrong)
- (void)tryAddInput:(AVCaptureInput *)input;
- (AVCaptureDeviceInput *)tryAddDeviceAsInput:(AVCaptureDevice *)device;

// Methods for easily adding devices as inputs
- (AVCaptureDeviceInput *)addRearCameraAsInput;
- (void)removeRearCameraAsInput;

- (AVCaptureDeviceInput *)addFrontCameraAsInput;
- (void)removeFrontCameraAsInput;

- (AVCaptureDeviceInput *)addAudioAsInput;

// Methods for easily adding output
- (void)tryAddOutput:(AVCaptureOutput *)output;
- (AVCaptureMovieFileOutput *)addFileOutput;

// Methods for mixing input and output
- (void)flipCamera;

@end

SimpleCaptureSession.m

//
// SimpleCaptureSession.m
//
// Copyright (c) 2013 Erik Ralston
//
// MIT License
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
//

#import "SimpleCaptureSession.h"

@interface SimpleCaptureSession()
{
    // Fields for holding onto inputs for devices
    AVCaptureDeviceInput *_rearCameraDeviceInput;
    AVCaptureDeviceInput *_frontCameraDeviceInput;
    AVCaptureDeviceInput *_audioDeviceInput;
}

@end

@implementation SimpleCaptureSession

#pragma mark - Input Device Properties

///
/// Gets the rear camera device
///
- (AVCaptureDevice *)rearCameraDevice
{
    return [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
}

///
/// Gets the front camera device
/// NOTE: Returns nil if no front camera found
///
- (AVCaptureDevice *)frontCameraDevice
{
    NSArray *devices = [AVCaptureDevice devicesWithMediaType:AVMediaTypeVideo];
    for (AVCaptureDevice *device in devices) {
        // Check if this is the front-facing camera
        if([device position] == AVCaptureDevicePositionFront)
        {
            // if we found it, then add it and return it
            return device;
        }
    }
    
    // if we didn't find it, return nil
    return nil;
}

///
/// Gets the microphone device
///
- (AVCaptureDevice *)audioDevice
{
    return [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeAudio];
}

#pragma mark - Helper Methods

///
/// Returns YES if the front camera is supported by the current device; otherwise, returning NO
///
- (BOOL)isFrontCameraSupported
{
    return [self frontCameraDevice] != nil;
}

///
/// Attempts to add the given input, logging an error if unable
///
- (void)tryAddInput:(AVCaptureInput *)input
{
    if ([self canAddInput:input])
        [self addInput:input];
    else
        NSLog(@"Couldn't add input device %@", input);
}

///
/// Tries to add the given device as an input, logging errors if problems occur
///
- (AVCaptureDeviceInput *)tryAddDeviceAsInput:(AVCaptureDevice *)device
{
    if (device) {
  	NSError *error;
		AVCaptureDeviceInput *videoIn = [AVCaptureDeviceInput deviceInputWithDevice:device error:&error];
		if (!error) {
			[self tryAddInput:videoIn];
            return videoIn;
		}
		else
			NSLog(@"Error trying to capture for device %@ with error %@", device, error);
	}
	else
		NSLog(@"Nil device passed, could not add");
    
    return nil;
}

///
/// Adds the video device as an input to the AVCaptureSession
///
- (AVCaptureDeviceInput *)addRearCameraAsInput
{
    // Setup Video Capture
	_rearCameraDeviceInput = [self tryAddDeviceAsInput:self.rearCameraDevice];
    return _rearCameraDeviceInput;
}

///
/// Removes the rear camera as an input
///
- (void)removeRearCameraAsInput
{
    [self removeInput:_rearCameraDeviceInput];
    _rearCameraDeviceInput = nil;
}

///
/// Tries to add the front-facing camera as an input for this device,
///
- (AVCaptureDeviceInput *)addFrontCameraAsInput
{
    // Try to find the front facing camera
    AVCaptureDevice *frontFacingCameraDevice = [self frontCameraDevice];
    
    // If we have a front-facing camera, then add it; otherwise, add the read camera
    if(frontFacingCameraDevice)
        _frontCameraDeviceInput = [self tryAddDeviceAsInput:frontFacingCameraDevice];
    else
        _frontCameraDeviceInput = [self addRearCameraAsInput];
    
    return _frontCameraDeviceInput;
}

///
/// Removes the front camera as an input
///
- (void)removeFrontCameraAsInput
{
    [self removeInput:_frontCameraDeviceInput];
    _frontCameraDeviceInput = nil;
}

///
/// Adds the audio device as an input to the AVCaptureSession
///
- (AVCaptureDeviceInput *)addAudioAsInput
{
    AVCaptureDevice *audioDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeAudio];
    return [self tryAddDeviceAsInput:audioDevice];
}

#pragma mark - Methods for Easy Output

///
/// Adds an output device, only if able, then logging if failed
///
- (void)tryAddOutput:(AVCaptureOutput *)output
{
    if([self canAddOutput:output])
        [self addOutput:output];
    else
        NSLog(@"Unable to add output %@", output);
}

///
/// Adds a capture movie file output to the current session
///
- (AVCaptureMovieFileOutput *)addFileOutput
{
    AVCaptureMovieFileOutput *movieFileOutput = [[AVCaptureMovieFileOutput alloc] init];
    [self tryAddOutput:movieFileOutput];
    return movieFileOutput;
}

#pragma mark - Methods for Input & Output

///
/// Flips the front and rear-facing camera, based on which one is currently in use
///
- (void)flipCamera
{
    if(_frontCameraDeviceInput)
    {
        [self removeFrontCameraAsInput];
        [self addRearCameraAsInput];
    } else {
        [self removeRearCameraAsInput];
        [self addFrontCameraAsInput];
    }
}

@end