VS web interface allows multiple TV episodes to be selected and the offline transcode option is available. This creates a list of the items which you then have to individually set the video quality from the pre-selected 'original'. Then set the batch going.
A quick look and I don't see where a default quality can be set.
On Mac I've installed Handbrake's command line tools and have a saved profile that I can apply to batches of files. Use Automator to create a dropper app with a script inside to take the dropped on files and convert each one. My script takes 50fps files and converts to 25fps.
There is a version of ffmpeg in VS, or somewhere in DSM, that probably could be used as a batch convertor.