> I am now looking to encode wav to mp4/aac i think i need to use the
> nero encoder for this

Not quite what you asked but ffmpeg is solid.  Converts pretty much
everything to anything.  Check out the list of supported file formats

http://www.ffmpeg.org/general.html#SEC3

If you used ffmpeg you wouldn't need different tools to convert to
different formats, so your program would have fewer dependencies.

Once I needed just to convert some files so I did something like:

# Not tested any of this tiny and flawed program
#
# Convert the file specified by path to a different multimedia format
def convert path, type
   `ffmpeg -i #{in_file} #{in_file}.#{type}`
end

convert "Rebecca Black - Friday.ogg", "mp3"
# That writes out to 'Rebecca Black - Friday.ogg.mp3'

This approach of calling the command line application probably isn't so
great if you were writing a big fancy program but it worked okay for my
little use case.

There is a work in progress gem here, but I haven't used it so cannot
comment https://github.com/gwik/ffmpeg-ruby

Good luck,
Johnny