StringAlong — Development Story

CLIENT

About the client

A "music education provider" leading string-instrument education.

The music education provider is a music education business offering teaching materials, scores and lessons for string players. It provides learning resources to a broad audience — amateur players, aspiring professionals and music-school students. Almost no learning app existed exclusively for string players, and scores, accompaniment and tutorials were scattered across separate services.

Built in-house around the concept of "an authentic ensemble experience even in solo practice" — a learning app exclusively for string players. Simultaneous iOS / Android development in Flutter, with semi-auto accompaniment implemented via a MusicXML parser and audioplayers. YouTube lesson videos play in sync with the score, and scores are sold through an IAP points model.

Supported instruments

4 (Vn/Va/Vc/Cb)

Sheet Music Library

1,000+ Pieces

Supported platforms

iOS + Android

BUSINESS FLOW

STEP

Score search

Discover scores by instrument, composer and difficulty

STEP

Buy Points

Acquire points via the App Store / Google Play

STEP

Score playback

Practice with semi-auto accompaniment + variable tempo

STEP

Lesson videos

YouTube tutorials linked to the score

CHALLENGE

Design challenges to solve

Four structural requirements the platform had to meet.

Every one is not a matter of technology choice but a business requirement tied directly to the learning experience, accompaniment quality, revenue model and user-acquisition speed.

① Without simultaneous iOS / Android development, user acquisition fragments

Release on only one platform, and you lose the other platform's users. A design that delivers an equivalent experience on both OSes is required.

② Ignore the MusicXML standard and your score assets can't scale

Manage scores in a proprietary format and importing external scores and integration with music publishers becomes difficult.

③ Implementing the IAP model yourself risks store-policy violations

Billing for digital goods must go through the App Store / Google Play. In-house payment gets rejected by the stores.

④ If lesson videos and scores aren't linked, the learning experience fragments

Open the score app and YouTube separately, and switching screens breaks concentration. A design for synced playback inside the app is required.

ARCHITECTURE

The architecture we built together

Turning the learning experience into an "unstoppable foundation" across four domains.

We built the music education provider's string-instrument learning platform in-house, from scratch. iOS / Android developed from a single Flutter codebase, with a Firebase backend centralizing auth, score delivery and notifications. Semi-auto accompaniment is implemented with a MusicXML parser + audioplayers.

Domain ①

Cross-platform

Challenge

Without simultaneous iOS / Android development, user acquisition fragments.

Solution

iOS / Android developed from one Flutter codebase

Riverpod state management + Hive local storage deliver an equivalent experience on both OSes

Domain ②

Score engine

Challenge

Ignore the MusicXML standard and your score assets can't scale.

Solution

Semi-auto accompaniment with a MusicXML parser + audioplayers

Parses notes from the industry-standard MusicXML and syncs the accompaniment track to the playback position

Domain ③

Billing model

Challenge

Implementing the IAP model yourself risks store-policy violations.

Solution

Points model with in_app_purchase + Firebase

Four packages sold via the App Store / Google Play, with bonuses; buy scores with points

Domain ④

Integrated learning experience

Challenge

If lesson videos and scores aren't linked, the learning experience fragments.

Solution

YouTube Player synced with the score

An embedded YouTube player in the app plays per-piece lesson videos without switching screens

TECH STACK

Mobile

Flutter

DartR RiverpodH Hive

Backend

FirebaseA Auth (Google/Apple/FB)S Storage · FirestoreM Messaging

Scores / Music

X MusicXML parser♪ audioplayers

YouTube Player$ in_app_purchase

IMPACT

The value the platform creates

The music education provider's "player learning experience" accelerates.

This foundation continuously produces business outcomes — not technical metrics — such as player retention, accompaniment quality and revenue stability.

① A foundation that maximizes learning retention

Semi-auto accompaniment + variable tempo lets players get an authentic ensemble experience even alone, making it easier to keep practicing.

② A design that makes score assets scalable

Compliance with the MusicXML standard allows importing scores from external publishers, enabling continuous library growth.

③ A structure that stabilizes the revenue model

Scores sold through an IAP points model. Routed via the App Store / Google Play, with no store-policy violation risk.

④ A design that concentrates the learning experience

Scores, accompaniment and YouTube lessons integrated into one screen — no screen switching, so concentration is maintained.

Solving "I have no practice partner" with a semi-auto accompaniment app.

A "music education provider" leading string-instrument education.

Four structural requirements the platform had to meet.

Turning the learning experience into an "unstoppable foundation" across four domains.

The music education provider's "player learning experience" accelerates.

Experience the music education provider through a live, working demo.