Handbrake RIP by Headless Ubuntu - Script to find DVD frame rate possible?

Hi All. My first post here after many years of enjoying the wealth of knowledge from all you guys on the forums so thanks for all your past help.

I have a headless media server Ubuntu 12.04 sever with Handbrake installed and script to auto run and rip when a DVD is inserted. This all works fine. However I have a problem with PAL DVD's of which my collection mostly consists.

Ripping region 1 NTSC disks produces MKV files that play fine in VLC and my WD network media players. Ripping PAL disks play fine in VLC but play fast on the hardware media players. I guess this is due to using the default in Handbrake that produces a variable frame rate flag. VLC knows what to do but the hardware players do not.

I can remux and change the flag to 25 frames but that sort of defeats the whole point of auto headless ripping your DVD collection and takes a long time.

So I have used --rate 25 on Handbrake to get over the problem for the moment but given the variety of PAL and NTSC DVD's in my collection a more elegant solution would be to run a script or application that checks the DVD, extract the frame rate and pass this as a variable to my script that runs Handbrake.

Has anyone come up with their own solution to this.

cheers
Andy

PS The heading wasn't meant to imply "RIP" rest in peace Handbrake :)