一年前我遇到了同样的问题。当我使用AVFoundation编写音频文件时，我没有看到任何元数据。我认为AVMetadataCommonKeyCreator不起作用。我现在不能说，但事实并非如此。

I've same problems about one year ago. I didn't see any metadata when I've wrote audio file using AVFoundation. I think that AVMetadataCommonKeyCreator doesn't work. I can't say about now but it was so.

我通过使用C库taglib来解决这个问题 http://taglib.github.com
为iOS构建这个库真的很容易。如果你不能编译它，我想你可以删除一些文件。

I solve this problem by using C library taglib http://taglib.github.com it's really easy to build this library for iOS. I think you can delete some files if you can't compile it.