Does it need internet?
Yes, mobile data on both phones. Voice uses very little. YouTube is video, so a two hour ride with music is roughly 300 to 500 MB per phone. A version that links two phones directly, with no signal at all, is planned for the app.
Why is music from YouTube and not Spotify?
Spotify does not let a web page or a small app play its music on phones. YouTube does, as long as the video stays visible, which is why the pillion's phone shows it. Some official music videos refuse to play outside YouTube. Lyric and karaoke uploads almost always work.
Does the music really get quieter on an iPhone?
In the browser, an iPhone ignores volume commands from web pages, so YouTube stays at one level there while everything else works. On Android and on a computer it lowers. The app fixes this by lowering your own music app through the phone itself.
Can we sing a duet?
Take turns. Bluetooth adds about a third of a second of delay, so two people singing at the same moment will always hear each other late. One singer at a time sounds right.
Will my earbud mic work at speed?
That depends on your earbuds and your helmet. Wind is the enemy. Xoundly takes wind and engine noise out of your voice before it is sent, which helps, but it cannot rescue a mic that is sitting in the full blast. Try a short ride first. If the mic struggles above 50 or 60 km/h, a helmet headset with a boom mic behind the chin bar is the fix, and Xoundly works with those too.
Is it safe and legal to use while riding?
Hands-free talk over Bluetooth is allowed under the Anti-Distracted Driving Act. Touching or reading your phone while moving is not. Set up while parked, keep transparency mode on so you still hear the road, and let the pillion handle the screen.