MPMoviePlayerViewController 播放本地视频一直loading

NSString * filePath = @"视频文件全路径";
NSURL * url = [NSURL URLWithString:filePath];
MPMoviePlayerViewController *moviePlayer = [[[MPMoviePlayerViewController alloc] initWithContentURL:url] autorelease];
[self presentMoviePlayerViewControllerAnimated:moviePlayer];

//NSURL * url = [NSURL URLWithString:filePath];
//应改为  fileURLWithPath
NSURL * url = [NSURL fileURLWithPath:filePath];