Had a look at this yesterday and hit a bit of a roadblock with getting the groovy script to run.
I think it's because the filters run during the "gather" phase but I'm using a local collection which doesn't use the gather phase. The logs show:
> Phase: Gathering content. (GatherPhase)
> skipped because Operation not supported on this collection type, in 0.2s
Is there a way to still run filters on local collections?
EDIT - Decided to just do the conversion in my XSLT before the files even hit funnelback.