Workflow with user-submitted files

Hello,

For my game Flaming Notes, the most requested feature is to have user-submitted songs.

I am looking at letting the user provide a MIDI file that will be parsed and the notes then generated. Is there a cross-platform way to let the user select a file? I know I can easily select a file in Android, not sure about iOS/Windows. Has anyone approached this issue?

One option is to provide a server for users to put MIDI files - but that can get messy (copyright, server costs, etc.). Another could be Google Drive/iCloud integration.

Comments? Thoughts?

Regards,
Kid