Current git now has experimental support for binary output via HP
Lab's DataSeries library. Feel free to give it a try. It generally
seems to work, but it hasn't seen much larger-scale testing yet. More
information here:
http://git.bro-ids.org/bro.git/blob_plain/HEAD:/doc/logging-dataseries.rst
(and soon also rendered on www.bro-ids.org once I've figured out why
it's not auto-updating ....)
Robin