Cross-Platform Sheet Music Viewer

I need a mobile application focused solely on letting musicians comfortably view and play their sheet music. Creation or heavy editing tools are not required; the experience should centre on smooth reading and accurate playback. I would like to be able to change the spacing between the lines, and reformat the music similar to an e-reader with font size change.

Scope
• Platforms: native or cross-platform code that compiles for both iOS and Android. The user experience must feel identical on each device.
• File support: open and render PDF scores with crisp zoom and page-turn gestures, and parse MusicXML so the player can follow the score and generate audio in real time.
• Core features: instant page turning, tempo control, simple looping of chosen bars, set-list builder, and offline storage of purchased or uploaded scores. If you already have tried-and-tested components for audio rendering, even better.

Tech notes
I am happy with Swift/SwiftUI + Kotlin, Flutter, or React Native, provided the PDF engine is fast and the MusicXML parser can handle large orchestral files. Mention any libraries—PDFKit, PSPDFKit, VexFlow, etc.—you intend to use.

Deliverables
1. iOS and Android builds ready for TestFlight / internal testing
2. Source code in a private Git repo with clear README for setup
3. A short video or live demo showing PDF and MusicXML playback working

Acceptance criteria
• A 200-page PDF and a 300-bar MusicXML file open within three seconds on an average device
• Playback stays in sync with the highlighted bar/beat while the user scrolls
• No crash after 30 minutes of continuous use

If parts of this scope need clarification, outline your questions alongside an estimated timeline and the technology stack you prefer.