This app was mentioned in 10 comments, with an average of 1.40 upvotes
Eu ia sugerir o Microsoft Groove. Ele reproduz músicas do OneDrive, então é só sincronizar, mas já que você usa o Ubuntu, tem o aplicativo Beat que tem a opção de usar o Dropbox. Como o Dropbox suporta Linux, acredito que você vá conseguir deixar tudo certinho. Boa sorte. :)
Edit: não usei o app, encontrei ele enquanto procurava uma alternativa grátis ao Cloud Player da doubleTwist. Talvez não tenha algum dos seus requisitos.
There's a few ones that use cloud storage like Dropbox or Google Drive to stream music from:
Beat: https://play.google.com/store/apps/details?id=de.stefanpledl.beat
CloudBeats: https://play.google.com/store/apps/details?id=com.cloudbeats
Here are a couple I found. I haven't tried most of them out, but they're out there.
There seem to be quite a few apps that seem to be able to do this.
Apple has an Apple Music Android app...
If you want something that can play straight from cloud storage then Beat should work.
You could try Beat.
Check out soundcloud.com. You're limited to 180 minutes on a free account with paid options for an increased limit or no limit.
Alternatively, you can upload to Dropbox/GoogleDrive and use an app like Vibe/Beat to stream it from there.
EDIT: Also check if your lecturer will be recording/making lectures available as I know mine did.