As the players with the source code exists (
.NET Implementation of an Ogg Vorbis Player[
^]), I don't see a problem with the encoder. Anyway, as Ogg Vorbis is Open Source (
http://www.vorbis.com/[
^]), anyone can compile its code and P/Invoke the required methods to use in C# project. Another way is C++/CLI project using available C++ code to create a .NET library which can be references as any .NET assembly. It may require some modification or mixed-mode (managed+unmanaged) C++/CLI + C++ library which can serve as .NET assembly.
—SA