Fix for Lookback (0.6.5) crash when recording is stopped while playing a movie with a MPMoviePlayerController

FixLookbackMPMoviePlayerControllerCrash.m

/**
 * Add these options to `OTHER_LDFLAGS` if Lookback is not linked to the app.
 *   -Wl,-U,_GFGetVersion
 *   -Wl,-U,_OBJC_CLASS_$_GFThumbnailer2
 *   -Wl,-U,_OBJC_IVAR_$_GFThumbnailer2._jobs
 *   -Wl,-U,_OBJC_IVAR_$_GFThumbnailer2._currentJob
 */
#import <AVFoundation/AVFoundation.h>
#import <MediaPlayer/MediaPlayer.h>
#import <dlfcn.h>
#import <objc/runtime.h>

#pragma clang diagnostic ignored "-Wdirect-ivar-access"
#pragma clang diagnostic ignored "-Wobjc-interface-ivars"
#pragma clang diagnostic ignored "-Wmissing-prototypes"

#pragma mark - Private Lookback Interfaces

__attribute__((weak_import)) extern NSString *(GFGetVersion)(void);

@interface GFThumbnailerJob : NSObject
- (NSURL *) url;
@end

__asm(".weak_reference _OBJC_IVAR_$_GFThumbnailer2._jobs");
__asm(".weak_reference _OBJC_IVAR_$_GFThumbnailer2._currentJob");
__attribute__((weak_import)) @interface GFThumbnailer2 : NSObject
{
@public
	NSMutableDictionary *_jobs;
	GFThumbnailerJob *_currentJob;
	MPMoviePlayerController *_controller;
}
- (void) jobFinished:(NSNotification *)notification;
- (void) _performNextJob;
- (void) _stopOutstandingThumbnailing;
@end

#pragma mark - _performNextJob Replacement

/**
 *  The original -[GFThumbnailer2 _performNextJob] method uses -[MPMoviePlayerController requestThumbnailImagesAtTimes:timeOption:]
 *  to generate a thumbnail. For some reason, this causes a crash when another MPMoviePlayerController is already playing a movie.
 *
 *  *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'movie player <MPMoviePlayerControllerNew: 0x1741f7b00> has wrong activation state (1)'
 *
 *  In order to avoid this crash, the `_performNextJob` method is rewritten to use `AVAssetImageGenerator` instead.
 */
static void PerformNextJob(GFThumbnailer2 *self, SEL _cmd)
{
	[self _stopOutstandingThumbnailing];
	self->_currentJob = [[self->_jobs allValues] firstObject];
	if (!self->_currentJob)
		return;
	
	NSURL *url = self->_currentJob.url;
	[self->_jobs removeObjectForKey:url];
	AVAsset *asset = [AVAsset assetWithURL:url];
	AVAssetImageGenerator *imageGenerator = [[AVAssetImageGenerator alloc] initWithAsset:asset];
	[imageGenerator generateCGImagesAsynchronouslyForTimes:@[ @3.0 ] completionHandler:^(CMTime requestedTime, CGImageRef imageRef, CMTime actualTime, AVAssetImageGeneratorResult result, NSError *error) {
		NSMutableDictionary *userInfo = [NSMutableDictionary new];
		UIImage *image = [UIImage imageWithCGImage:imageRef];
		if (image)
			userInfo[MPMoviePlayerThumbnailImageKey] = image;
		if (error)
			userInfo[MPMoviePlayerThumbnailErrorKey] = error;
		
		NSNotification *notification = [[NSNotification alloc] initWithName:MPMoviePlayerThumbnailImageRequestDidFinishNotification object:nil userInfo:[userInfo copy]];
		[self performSelectorOnMainThread:@selector(jobFinished:) withObject:notification waitUntilDone:NO];
	}];
}

@implementation GFThumbnailer2 (FixLookbackMPMoviePlayerControllerCrash)

+ (void) load
{
	@autoreleasepool
	{
		if (!GFGetVersion)
		{
			NSLog(@"Could not fix Lookback/MPMoviePlayerController crash because the GFGetVersion function was not found.");
			return;
		}
		
		NSSet *supportedVersions = [NSSet setWithArray:@[ @"0.6.5" ]];
		NSString *lookbackVersion = GFGetVersion();
		if (![supportedVersions containsObject:lookbackVersion])
		{
			NSLog(@"Could not fix Lookback/MPMoviePlayerController crash because version %@ is not supported.", lookbackVersion);
			return;
		}
		
		Method _performNextJob = class_getInstanceMethod(self, @selector(_performNextJob));
		method_setImplementation(_performNextJob, (IMP)PerformNextJob);
	}
}

@end