Real-Time Digital Signage Platform

I need a full digital-signage solution that can play videos, images, and text/announcements on any connected screen. My priority is the ability to push updates instantly, so the platform must refresh content in real time rather than on a schedule... (Budget: $750 - $1500 USD, Jobs: Flutter, HTML, Mobile App Development, Node.js, PHP, User Interface / IA, Web Development, Website Design)