试图获取视频缩略图

Question

我想从保存在Documents /文件夹中的视频获取视频缩略图，并将其显示在UITableViewCell中的UIImageView中。这里是我的函数来获取缩略图：

- (UIImage*) thumbnailImageForVideo:(NSURL *)sourceURL 
{ 
    AVAsset *asset = [AVAsset assetWithURL:sourceURL]; 
    AVAssetImageGenerator *imageGenerator = [[AVAssetImageGenerator alloc]initWithAsset:asset]; 
    NSError *err = NULL; 
    CMTime time = CMTimeMake(1, 1); 
    CGImageRef imageRef = [imageGenerator copyCGImageAtTime:time actualTime:NULL error:&err]; 
    NSLog(@"err==%@, imageRef==%@", err, imageRef); 
    UIImage *thumbnail = [[UIImage alloc] initWithCGImage:imageRef]; 
    CGImageRelease(imageRef); // CGImageRef won't be released by ARC 
    return thumbnail; 
} 

而且这里是我使用它：

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath 
{ 
    LibraryCell *libraryCell = [tableView dequeueReusableCellWithIdentifier:@"LibraryCell" forIndexPath:indexPath]; 

    NSString *videoPath = [NSString stringWithFormat:@"%@/%@", [NSHomeDirectory() stringByAppendingPathComponent:@"Documents"], [libraryFiles objectAtIndex:indexPath.item]]; 
    libraryCell.itemImage.image = [self thumbnailImageForVideo:[NSURL URLWithString:videoPath]]; 

    return libraryCell; 
} 

的应用程序不会崩溃，但没有图像。这是我在控制台中看到：

2013-04-13 23:44:46.828 GeekOut[14433:907] err==Error Domain=NSURLErrorDomain Code=-1 "unknown error" UserInfo=0x1f0b4610 {NSUnderlyingError=0x1f0b3220 "The operation couldn’t be completed. (OSStatus error -12935.)", NSLocalizedDescription=unknown error}, imageRef==(null) 
2013-04-13 23:44:46.859 GeekOut[14433:907] err==Error Domain=NSURLErrorDomain Code=-1 "unknown error" UserInfo=0x1dd8c660 {NSUnderlyingError=0x1dd8c5c0 "The operation couldn’t be completed. (OSStatus error -12935.)", NSLocalizedDescription=unknown error}, imageRef==(null) 
2013-04-13 23:44:46.893 GeekOut[14433:907] err==Error Domain=NSURLErrorDomain Code=-1 "unknown error" UserInfo=0x1f0bec80 {NSUnderlyingError=0x1f0be9b0 "The operation couldn’t be completed. (OSStatus error -12935.)", NSLocalizedDescription=unknown error}, imageRef==(null) 

Answer 1

你的缩略图提取代码工作正常。问题是你正在初始化NSURL的方式tableView：cellForRowAtIndexPath：。

尝试修改此：

[NSURL URLWithString:videoPath] 

要这样：

[NSURL fileURLWithPath:videoPath]