Vorbis dev - Jul 2015 - Question about changing default metric for codebooks

I wanted to try improving the compression efficiency of libvorbis by
specifying a new metric used in generating the codebooks.

I'm not sure how to compile new codebook entries in the vq directory. 
I'm guessing you do something to the '.vqs' files to get the
codebook
'.h' files that replace the ones in the libvorbis 'books'
directory.
Also, I was wondering how those '.h' files were generated, were the
trained on audio data?  If so, is that audio training data available?  I
would like to rebuild these codebook files exactly as they were but
using a new metric (instead of the default Euclidean metric) and compare
the results.  Any information, would be greatly appreciated.

Thanks,
Tony