In 2019, I built and patented a system for handling 100+ mobile devices in a single physical room with all microphones and speakers active. Mixed Android and iOS, multiple models and OS versions, running over WebRTC. Deployed at scale to replace hardware Cisco conference phones with mobile-device hubs in meeting rooms.
The hard part isnโt just multi-mic feedback amplification. Itโs that even when one person speaks, their voice reaches each deviceโs microphone at slightly different times because the distance from the speaker to each device varies. At room scale thatโs tens of milliseconds of differential propagation. Transmit all N mic streams upstream without coordination and you get audible comb-filtering and ghosting. Play received audio on all N speakers without sync and the same effect runs in reverse.
The architecture is ๐ฅ๐๐๐๐๐ซ-๐๐ฅ๐ข๐๐ง๐ญ ๐๐จ๐จ๐ซ๐๐ข๐ง๐๐ญ๐ข๐จ๐ง ๐ฉ๐๐ซ ๐๐๐จ๐ฎ๐ฌ๐ญ๐ข๐ ๐ซ๐จ๐จ๐ฆ. ๐๐ง ๐ญ๐ก๐ ๐ฆ๐ข๐ ๐ฌ๐ข๐๐, a selection algorithm picks the device with the best signal in real time and only that device transmits upstream. ๐๐ง ๐ญ๐ก๐ ๐ฌ๐ฉ๐๐๐ค๐๐ซ ๐ฌ๐ข๐๐, the leader synchronizes playback timestamps across clients so the same audio frame plays at the same wall-clock moment on every device. US patent: โMethod and System for Teleconferencing Using Coordinated Mobile Devicesโ (https://patents.justia.com/inventor/muhammad-usman-bashir).
๐๐๐๐๐ง๐ญ๐ฅ๐ฒ we at RTC LEAGUE extended the LiveKit Android and iOS client SDKs to add this coordination layer for a different use case: distributed media playback. The mic-selection-and-sync primitive generalizes naturally. ๐๐๐ฆ๐จ: a grid of mobile devices playing the same YouTube video frame-synced across all of them, effectively turning a stack of phones into a coordinated mobile-device billboard.
๐๐จ๐ฎ๐๐ฎ๐๐ ๐ฌ๐จ๐ฎ๐ซ๐๐ ๐ฎ๐ฌ๐๐ ๐ข๐ง ๐ญ๐ก๐ ๐๐๐ฆ๐จ: https://www.youtube.com/watch?v=lgm3puP3tMA
๐๐ฒ๐ง๐๐๐ ๐ฆ๐ฎ๐ฅ๐ญ๐ข-๐๐๐ฏ๐ข๐๐ ๐ฉ๐ฅ๐๐ฒ๐๐๐๐ค ๐๐๐ฆ๐จ: https://drive.google.com/file/d/1NTtyiz3lLATnwbaYdFNXkE2UquxBbj_F/view?usp=sharing
The primitives generalize across acoustic feedback elimination, conference room mic selection, and distributed media sync. Happy to dig into any of it if it overlaps with what others are building.