DND5e DPS Meter ( I know I know...)

So in our campaign I have the odd need to allow my players to rapidly throw out damage during a specific encounter. Easy enough for them as they can just click macros and buttons on their sheets but I need a way to capture the sum total of damage they deal over the course of a minute or 2. Since this will be flying up the chat window I wont be able to track it. preferably in a running total so I can see the numbers fly (right? I mean cmon. That's awesome).

If they are all using the character sheet, you could create a script that looks at the chat and captures the damage fields of the issues Roll Templates. It gets harder if you need to check if the attack was successful or the targeted creature saved or the lije. 

It would be against a specific creature so I could hard code the AC. how to capture the attack roll and the dmg would be the question.

Roll Templates go to chat as a series of {{ }} wrapped key-value pairs. Expanding inline rolls to their value first, you’d need to parse those key-value pairs to build a lookup of sorts, then check whatever key corresponds to the attack against the AC. On success you’d find the keys corresponding to damage and add them. You’ll need to know how you will handle advantage/disadvantage and you might need to duplicate some of the display logic of the roll template to know if certain parts apply (critical hits, divine strike, etc). All in all, not terribly easy to get right.