It looks like the 64 bit version of the Windows Media Format SDK .lib static library files are not where you would expect to find them. If you go to the Windows Media SDK downloads page, there is a happy little link for the Windows Media Format 11 SDK (link below). This link does not detail a specific platform supported by the download. Because of this the assumption is that this link will allow you to download the SDK for all platforms. I got caught in this trap too. Unfortunately this is not the case.

The link on the Windows Media download page is for XP SP2 / SP3 only. This download is not intended to be used on Windows Vista. Luckily if you accidently download this version of the SDK and install it on Vista and use it to build your application, you are safe as long as you are building against x86. If you want to target x64 on Vista this download is not going to work for you. In other words, if you are building against the WM Format SDK on Vista, don’t use the Windows Media Format 11 SDK link on the Windows Media Download page. This download is intended for XP SP2 / 3 only.

Question: So what do I use if I want to build against the Windows Media Format 11 SDK on Vista? Answer: The Windows SDK for Windows Server 2008 and .net Framework 3.5 (link below).

It looks like we have bundled all of the WM Format SDK libraries into the latest version of the Windows SDK (formerly Platform SDK). For whatever reason the information on the Windows Media download page does not mention this. According to the documentation on this download page the WM Format components are not included in the Windows SDK. The good news is that the Windows SDK is now a “one stop shop” for all your Windows Media needs.
 

Reference:

Windows Media Format 11 SDK for XP x86 & x64
http://download.microsoft.com/download/a/c/3/ac367925-39e7-4451-a175-a224f94fbdce/wmformat11sdk.exe

Windows SDK for Windows Server 2008 and .NET Framework 3.5
http://www.microsoft.com/downloads/details.aspx?familyid=F26B1AA4-741A-433A-9BE5-FA919850BDBF&displaylang=en