Sheng Jiang 蒋晟

User IMFCoder wants to know how to solve a LNK2001 error related to CLSID_CMpeg4sDecMediaObject. The user has no problem linking a lib file in the project but couldn’t find which lib the CLSID is in.

The Windows SDK is strangely cryptic on which lib file the CLSID is exported from. Luckily you can find out the library file you need to link with, if you execute the following command line in the SDK command prompt

Update: use findstr /m /S /c:”CMpeg4″ *.lib
is easier  

C:\Program Files\Microsoft SDKs\Windows\v7.0\Lib>for %a in (*.lib) do dumpbin /symbols %a |find “CMpeg4”

After a bunch of fruitless searches, the search yields the results when it encounters wmcodecdspuuid.lib

C:\Program Files\Microsoft SDKs\Windows\v7.0\Lib>dumpbin /symbols wmcodecdspuuid.lib   | find “CMpeg4”
056 00000000 SECT1D notype       External     | _CLSID_CMpeg4DecMediaObject
059 00000000 SECT1E notype       External     | _CLSID_CMpeg43DecMediaObject
05C 00000000 SECT1F notype       External     | _CLSID_CMpeg4sDecMediaObject
05F 00000000 SECT20 notype       External     | _CLSID_CMpeg4sDecMFT
065 00000000 SECT22 notype       External     | _CLSID_CMpeg4EncMediaObject
068 00000000 SECT23 notype       External     | _CLSID_CMpeg4sEncMediaObject

There is a big uuid.lib file contains most of the SDK CLSIDs in the Windows SDK, and it is likely linked by default if you use Visual C++’s project templates, so you may not see the link error at all if you use common CLSIDs like CLSID_InternetExplorer.

There are also GUIDs defined in the Windows SDK using the DEFINE_GUID macro. The SDK assumes you to initialize the GUID using the methods demonstrated in How to avoid error “LNK2001 unresolved external” by using DEFINE_GUID.