This is very similar to this:

https://github.com/xupefei/XNA-4.0-Content-Compiler

except the code is refactored to be a little cleaner (IMO) and I've added in command line functionality so you can use it via build scripts like rake or whatever you enjoy using.

• build (Input Directory) (Output Directory) Builds all files in the input directory and places them into the output directory

• build-file (Input File) (Output File) Builds a file and outputs it to the output file

• watch (Input Directory) (Output Directory) Watches a directory for file changes and rebuilds changed files

• help Prints each command and a description

• Image Files: *.bmp, *.jpg, *.png, *.tga, *.dds
• Audio Files: *.wav, *.mp3, *.wma
• SpriteFont Files: *.spritefont There are more types that are supported by the XNA Content Pipeline, but they do not have all the UI features yet. If you need a new type, just create an issue or pull request.

There are a few caveats here, namely the watch command isn't implemented yet and anything ending with .xml, .ini or .config gets 1 to 1 copied from the input to the output directory. This is because I personally like using flat text files in some of my projects and don't want to have to copy them manually.

Lastly, since this uses MSBuild I couldn't get it to build on Mono or run in XBuild. This makes it tricky to use on things like Linux based build servers.

If you want to take a stab at implementing the file watch stuff, be my guest and submit a pull request.