objective-c - 为什么 AVAssetExportSession 会产生一个空文件？

Question

我正在尝试从 UIImagePickerController 创建的源视频中导出 .mov 文件。问题是 AVAssetExportSession 创建的输出文件只有 668 字节。为什么会失败？我的代码:

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
{
    NSURL *imagePickerVideoURL = [info objectForKey:UIImagePickerControllerMediaURL];
    NSString *filename = @"vid1.mov";

    AVAsset *video = [AVAsset assetWithURL:imagePickerVideoURL];
    AVAssetExportSession *exportSession
      = [AVAssetExportSession exportSessionWithAsset:video presetName:AVAssetExportPresetMediumQuality];
    exportSession.shouldOptimizeForNetworkUse = YES;
    exportSession.outputFileType = AVFileTypeQuickTimeMovie;
    exportSession.outputURL = [pathToSavedVideosDirectory URLByAppendingPathComponent:filename];
    NSLog(@"processing video...: %@", exportSession);
    [exportSession exportAsynchronouslyWithCompletionHandler:^{
                       NSLog(@"done processing video!");
                   }];
}

Answer 1

我猜这是因为 exportSession 没有保留在内存中，因此在 didFinishPickingMediaWithInfo 完成后(在导出 session 完成处理程序运行之前)被杀死。

将 exportSession 存储到 @property 或更改完成处理程序以复制对 exportSession 的引用，如下所示:

[exportSession exportAsynchronouslyWithCompletionHandler:^{
       if (AVAssetExportSessionStatusCompleted == exportSession.status)
       {
           NSLog(@"done processing video!");
       }
}];