Synced play: every device downloads the song and plays it locked to a shared clock — tightest sync, no streaming, any browser. Library stream: host streams the playing file over WebRTC. Tab audio: for YouTube — Chrome/Edge only, pick this tab and tick “Also share tab audio”. Streams as 48 kHz stereo Opus and carries the live YouTube timecode to every device in the room.
Scan with another phone to open this room. On that phone, tap Join as a speaker.