根据推送通知指南:

您可以将音频数据打包到 aiff、wav 或 caf 文件中.然后，在Xcode，将声音文件作为非本地化资源添加到您的项目中应用程序包.

You can package the audio data in an aiff, wav, or caf file. Then, in Xcode, add the sound file to your project as a nonlocalized resource of the application bundle.

它没有提及 MP3.我使用了有效的 aif 文件.我会坚持 Apple 指定的内容.

It doesn't say anything about MP3s. I've used aif files which worked. I'd stick to what Apple specifies.