[mushishi]

This is what Yousician does for singing (and other analog instruments) but unfortunately not for the violin: https://yousician.com/singing

Haven't tried it but maybe the following app could help?

> Trala uses signal processing, groundbreaking technology that analyzes the sound of your violin and gives you instant feedback on pitch and rhythm every time you practice. When you play the wrong notes, we’ll help you get back on track.

https://www.trala.com/ (I just remembered it being recommended somewhere.)