typically a plug in would allow you to use different formats that are not supported as standard (e.g wav, mp3, flac etc etc)...
... having spent a bit of time researching the options around a windows home server i have been investigating the media server options as the WHS media server will not serve flac audio files. this is a pain as most of my music is in that format.
It turns out that its possible to use other upnp media servers hosted on the WHS, the option i have found include a number of unpnp media servers that support flac files, these include Twonky (which does have a plug in designed for WHS), FUPPES & tversity, all of which support flac
so just as im trying to narrow down the options , i started thinking about what video formats i need as well as do i need transcoding?... i currently use my movies as a plug in to vista media centre which works wonderfully and its also compatable with WHS :D , this handles the storing and selection of movies so cant really see that i will need to have any transcoding done when i have dedicated pc's/media centres wherever i want to watch anything.
Given my video is a variety of formats (mpeg 2 & 4 including TS & VOB file structures, avi, xvid, dixv & 1 mkv) and it all plays perfectly wherever i watch it i think im going to use the WHS for backing up my video and for serving my pictures and music, hopefully that will be a simple way forward