为什么AVAssetImageGenerator generateCGImagesAsynchronouslyForTimes崩溃了应用程序

我想使用generateCGImagesAsynchronouslyForTimes从video中提取每秒2帧。 但我的应用程序崩溃。 我正在监视内存使用情况，但不超过14 MB。

这里是代码：

 - (void) createImagesFromVideoURL:(NSURL *) videoUrl atFPS: (int) reqiuredFPS completionBlock: (void(^) (NSMutableArray *frames, CGSize frameSize)) block { NSMutableArray *requiredFrames = [[NSMutableArray alloc] init]; AVURLAsset *asset = [[AVURLAsset alloc] initWithURL:videoUrl options:nil]; AVAssetImageGenerator *generator = [[AVAssetImageGenerator alloc] initWithAsset:asset]; generator.requestedTimeToleranceAfter = kCMTimeZero; generator.requestedTimeToleranceBefore = kCMTimeZero; generator.appliesPreferredTrackTransform = YES; UIImage *sampleGeneratedImage; for (Float64 i = 0; i < CMTimeGetSeconds(asset.duration) * reqiuredFPS ; i++) { CMTime time = CMTimeMake(i, reqiuredFPS); NSError *err; CMTime actualTime; CGImageRef image = [generator copyCGImageAtTime:time actualTime:&actualTime error:&err]; if (! err) { sampleGeneratedImage = [[UIImage alloc] initWithCGImage:image]; break; } } //Get the maximum size from 1 frame generator.maximumSize = [self getMultipleOf16AspectRatioForCurrentFrameSize:sampleGeneratedImage.size]; NSMutableArray *requestedFrameTimes = [[NSMutableArray alloc] init]; for (Float64 i = 0; i < CMTimeGetSeconds(asset.duration) * reqiuredFPS ; i++) { CMTime time = CMTimeMake(i, reqiuredFPS); [requestedFrameTimes addObject:[NSValue valueWithCMTime:time]]; } [generator generateCGImagesAsynchronouslyForTimes:[requestedFrameTimes copy] completionHandler:^(CMTime requestedTime, CGImageRef _Nullable image, CMTime actualTime, AVAssetImageGeneratorResult result, NSError * _Nullable error) { if (image) { UIImage *generatedImage = [UIImage imageWithCGImage:image]; [requiredFrames addObject:generatedImage]; } if (CMTimeCompare(requestedTime, [[requestedFrameTimes lastObject] CMTimeValue]) == 0) { NSLog(@"Image processing complete"); dispatch_async(dispatch_get_main_queue(), ^{ block(requiredFrames, generator.maximumSize); }); } else { NSLog(@"Getting frame at %lld", actualTime.value/actualTime.timescale); } }]; }