C# C+ / Ffmpeg, Libav developer needed

Introduction: FFmpeg can read various raw audio types (sample formats) and demux or mux them into different containers (formats). For example, you can read and write raw pcm audio into a wav container. Or convert between raw types.
Specifications:
• Write a method in C# to take an input audio stream in any format supported by FFmpeg or Libav and converts it to an output stream with decoded audio in 8 kHz, 16 bit, mono (PCM, raw audio).
• The code should change the physical frame structure and header according to the new container.
• The code should be C# (alternatively, purely managed C++ is also acceptable).
• It should be possible to instantiate multiple instances of above classes and use them at the same time.
Public class Converter
{
Public Void Execute(Stream inputStream, Stream outputStream)
{
//code here
}
}
• Try not to attempt to read all data into memory.
• Code should consume less cpu resource.
• Code should work with the latest version of the ffmpeg/ libav library.

Deliverables: Should include complete sln, csproj and all needed cs files.