Yes Now Windows User also can share Audio & Video files via WhatsApp.
Windows phone 8.1 users are now able to send audio & video files.
Just download this app and beat the android users who say Windows user can't send audio files using WhatsApp
http://www.windowsphone.com/en-us/store/app/what-appshare/8b9eb104-3ab8-43f1-ad19-50bbcb8027ce