The boot animation is stored in a WIM file and to replace it the Microsoft WIM library is necessary. Unfortunately the only official Microsoft downloads containing them are the Windows AIKs which are over a gigabyte download and require you to burn a DVD (or have an ISO mounter). However there are sources on the Internet with these files in smaller packages. Below is how to use either.

Using Microsoft Windows AIK

1. Download the Windows AIK (1.3GB)
2. Burn the ISO to a DVD or mount the ISO
3. Install the Windows AIK
4. Copy "wimgapi.dll" from "C:\Program Files\Windows AIK\Tools\x86" (32-bit) or "C:\Program Files\Windows AIK\Tools\amd64" (64-bit) to the System32 folder or the folder with Win7BootUpdater.exe

Using a 3rd Party Distribution

1. Download a package that contains wimgapi.dll, wimfltr.inf, and wimfltr.sys for your system (32 or 64-bit). Since it violates copyright law I cannot host them here and links are always changing. Search Google for "WIM Filter Download".
2. Extract the package
3. Right-click "wimfltr.inf" and choose "Install" (no messages means success)
4. Copy "wimgapi.dll" to the System32 folder or the folder with Win7BootUpdater.exe

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