iOS7中的AVAssetImageGenerator随机失败

Question

我有一个AVComposition和一个AVVideoComposition,我每半秒左右就生成一个拇指视频.我使用动画工具进行一些叠加.我在操作队列上执行调用,并在某些类型的编辑后触发.操作队列是串行而不是异步,因此进程永远不会运行并且我已经验证了这一点.下面的代码在串行队列中的另一个NSOperation中的主线程上执行.

现在我的问题是,拇指随机失败,没有模式.我可以运行一次并让它全部成功.我可以用完全相同的参数再次运行它,并且有一些拇指失败.我可以再次运行它并且有不同的拇指失败.

它似乎与其他线程中正在进行的其他活动有关,例如从ALAssetLibrary或MediaFramework查询大量项目.

我还要提到这在iOS6中没有这个问题.

在生成拇指之前,我会创建AVComposition和AVVideoComposition的副本.

有人对我有任何指示？

我很感激.

//this must be called on the main thread to correctly generate overlays
[[NSOperationQueue mainQueue] addOperationWithBlock:^{

    AVAsset *asset = avComposition;

    AVAssetImageGenerator *generator = [[AVAssetImageGenerator alloc] initWithAsset:asset];
    generator.appliesPreferredTrackTransform = TRUE;

    AVMutableVideoComposition *mutableVideoComposition = (AVMutableVideoComposition *) avVideoComposition.mutableCopy;
    CALayer *baseSyncLayer = [CALayer layer];
    baseSyncLayer.frame = CGRectMake(0, 0, resolution.width, resolution.height);
    CALayer *videoLayer = [CALayer layer];
    videoLayer.frame = CGRectMake(0, 0, resolution.width, resolution.height);
    [baseSyncLayer addSublayer:videoLayer];
    __unused NSArray *imageLayers = [MovieCompositionService applyImageAnimations:avComposition andLayer:baseSyncLayer andProject:project fileRender:YES addTextOverlays:addTextOverlays andResolution:resolution];
    mutableVideoComposition.animationTool = [AVVideoCompositionCoreAnimationTool videoCompositionCoreAnimationToolWithPostProcessingAsVideoLayer:videoLayer inLayer:baseSyncLayer];
    generator.videoComposition = mutableVideoComposition;

    NSMutableArray *images = [[NSMutableArray alloc] init];

    __block BOOL hasErrors = NO;

    AVAssetImageGeneratorCompletionHandler handler = ^(CMTime requestedTime, CGImageRef im, CMTime actualTime, AVAssetImageGeneratorResult result, NSError *error) {
        if (!hasErrors) {

            DDLogVerbose(@"ACTUAL GENERATION TIME %f", CMTimeGetSeconds(actualTime));

            if (result != AVAssetImageGeneratorSucceeded) {
                DDLogError(@"Failed to generate thumb: %@", error.localizedDescription);
                hasErrors = YES;
                [generator cancelAllCGImageGeneration];
                finishBlock(images, YES);
            } else {
                [images addObject:[UIImage imageWithCGImage:im]];

                if (CMTIME_COMPARE_INLINE(requestedTime, ==, ((NSValue *) timeIntervals.lastObject).CMTimeValue)) {
                    DDLogVerbose(@"Movie composition thumb generation complete");
                    finishBlock(images, NO);
                }
            }
        }
    };

    generator.maximumSize = thumbSize;
    [generator generateCGImagesAsynchronouslyForTimes:timeIntervals completionHandler:handler];
}];

Answer 1

我使用以下内容来生成缩略图。

- (void)getThumbnailImageForTime:(float)instance_time withCompletion:(void(^)(UIImage *))completion
{
    dispatch_queue_t queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0ul);
    dispatch_async(queue, ^{
        __block UIImage *thumb ;
        AVPlayerItem *playerItem = [AVPlayerItem playerItemWithURL:self.videoUrl];
        AVAssetImageGenerator *_generator;
        _generator = [AVAssetImageGenerator assetImageGeneratorWithAsset:playerItem.asset];

        AVAssetImageGeneratorCompletionHandler handler = ^(CMTime requestedTime, CGImageRef image, CMTime actualTime, AVAssetImageGeneratorResult result, NSError *error) {
            if (result == AVAssetImageGeneratorSucceeded) {
                thumb = [UIImage imageWithCGImage:image];
                NSLog(@"Succesfully generater the thumbnail!!!");
            } else {
                NSLog(@"Failed to generater the thumbnail!!!");
                NSLog(@"Error : %@",error.localizedDescription);
                [self performSelector:@selector(retryingThumbnialGeneration) withObject:nil afterDelay:1.0f];
            }
            dispatch_async(dispatch_get_main_queue(), ^{
                 completion(thumb);
            });
        };

        [_generator generateCGImagesAsynchronouslyForTimes:[NSArray arrayWithObject:[NSValue valueWithCMTime:CMTimeMakeWithSeconds(2,10)]] completionHandler:handler];

    });

}