从线程中的视频网址中提取缩略图
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【中文标题】从线程中的视频网址中提取缩略图【英文标题】:Extract thumbnail from video url in threads 【发布时间】:2014-01-10 21:11:35 【问题描述】:我在另一个线程中的 MPMoviePlayer 出现问题,使用 (Grand Central Dispatch)。我想通过 url 吸引视频,剪切第 5 帧并返回图片。在模拟器中工作正常,但在真实设备上 - 下降。这里有什么问题?也许它只适用于主线程?
NSURL* url = [NSURL URLWithString:filePath];
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^(void)
MPMoviePlayerController* moviePlayer = [[MPMoviePlayerController alloc] initWithContentURL:url];
moviePlayer.shouldAutoplay = NO;
UIImage* thumbnail = [moviePlayer thumbnailImageAtTime:5 timeOption:MPMovieTimeOptionNearestKeyFrame];
dispatch_async(dispatch_get_main_queue(), ^(void)
[[Singleton sharedSingleton].imageCache setValue:thumbnail forKey:filePath];
[cell.presentationViewOutlet setImage:thumbnail];;
);
);
现在,我尝试使用另一种方法,但它也在模拟器上运行良好,并且在真实设备上不显示。有时返回imageRef = (null)
,有时返回imageRef = <CGImage 0x1766dd20>
。
编辑:
NSURL* url = [NSURL URLWithString:filePath];
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^(void)
AVAsset *asset = [AVAsset assetWithURL:videoURL];
AVAssetImageGenerator *imageGenerator = [[AVAssetImageGenerator alloc]initWithAsset:asset];
imageGenerator.appliesPreferredTrackTransform = TRUE;
CMTime time = CMTimeMakeWithSeconds(1, 1);
NSError *err = NULL;
CGImageRef imageRef = [imageGenerator copyCGImageAtTime:time actualTime:NULL error:&err];
dispatch_async(dispatch_get_main_queue(), ^(void)
NSLog(@"imageRef = %@", imageRef);
UIImage* image = [UIImage imageWithCGImage:imageRef];
if (image != nil)
NSLog(@"image != nil");
[view setImage:image];
NSString* videoURLString = [videoURL absoluteString];
[[Singleton sharedSingleton].imageCache setValue:image forKey:videoURLString];
CGImageRelease(imageRef);
else
NSLog(@"err = %@", err);
);
);
错误:
如果 imageRef = (null) 显示 err = Error Domain=AVFoundationErrorDomain Code=-11800 "The operation could not be completed" UserInfo=0x156c1a50 NSLocalizedDescription=The operation could not be completed, NSUnderlyingError=0x155b29a0 "The operation couldn’t be completed. (OSStatus error -12792.)", NSLocalizedFailureReason=An unknown error occurred (-12792)
【问题讨论】:
你找到解决这个问题的方法了吗?我现在也面临同样的问题:( @VishnuKumar.S 您找到解决方案了吗?面临同样的问题:(***.com/questions/37374008/… 【参考方案1】:MPMoviePlayerController 是一个用户界面控制器。因此,几乎可以肯定它不是线程安全的。文档没有具体说明,但我敢打赌它不是。
【讨论】:
什么样的问题? 不可预测,有时返回 imageRef = (null),有时返回 imageRef =如果将 imageref 移到 async 部分内会更好吗?喜欢:
NSURL* url = [NSURL URLWithString:filePath];
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^(void)
AVAsset *asset = [AVAsset assetWithURL:videoURL];
AVAssetImageGenerator *imageGenerator = [[AVAssetImageGenerator alloc]initWithAsset:asset];
imageGenerator.appliesPreferredTrackTransform = TRUE;
CMTime time = CMTimeMakeWithSeconds(1, 1);
dispatch_async(dispatch_get_main_queue(), ^(void)
NSError *err = NULL;
CGImageRef imageRef = [imageGenerator copyCGImageAtTime:time actualTime:NULL error:&err];
NSLog(@"imageRef = %@", imageRef);
UIImage* image = [UIImage imageWithCGImage:imageRef];
if (image != nil)
NSLog(@"image != nil");
[view setImage:image];
NSString* videoURLString = [videoURL absoluteString];
[[Singleton sharedSingleton].imageCache setValue:image forKey:videoURLString];
CGImageRelease(imageRef);
else
NSLog(@"err = %@", err);
);
);
【讨论】:
是的显示,但是现在主线程很忙所有界面在加载图像之前都是不可点击的。以上是关于从线程中的视频网址中提取缩略图的主要内容,如果未能解决你的问题,请参考以下文章