Feerless: Crowd-sourced, preemptive notifications for Netflix watchers with PTSD
feerless.us
feerless.us
Maybe you could talk to these guys who have done exactly that for figuring out viewership numbers (maybe they'll want to share the tech): http://www.wired.com/2016/01/meet-symphony-the-company-that-...
Or maybe see if you can use http://echoprint.me/ or build your own http://royvanrijn.com/blog/2010/06/creating-shazam-in-java/
[EDIT]: Or maybe a wearable app, so that you don't have to have your phone out? It could potentially warn you about TV/movies too just by vibrating.
To be more specific, do users set their triggering scenarios in the extension (eg shark attacks and water but not clowns) and only recieve warnings for that type of trigger, or are all reported triggers displayed to all users?
(though how would one categorize clowns attacking sharks??)
Thank you for the clarification, best of luck with your project.