Some thoughts about Classical Music on Smartphone:
Why is this an issue at all? Aren't there hundreds of apps for playing locally stored music files?
Yes, there are, but all those I tested share the same design flaw: They are exclusively developed for pop music. All music is a "Song" and is named "I. Allegro" or similar. Longer album or performer names (called "artists", due to pop music) are truncated with "...", and only a few apps know about "composers", and none I tested knows about works and movements.
All these limitations do not have a technical reason, but maybe a cultural one: Software developers even in large companies like Google seem to know nothing about classical music.
To fill this gap I wrote two Android apps (porting to iOS is planned) that do not have any of the mentioned limitations (and besides, they also play pop music if necessary!). Unfortunately nobody knows about them, and they also cannot be found by Google Search (for whatever reason). This is really a pity, because the development effort was immense, and they are free of advertisements, the first one being free, the larger one for a small donation. Note that this text you are reading is no hidden advertisement to gain money: Just write an email to the developer email address (visible in the Play Store) and ask for a voucher!
The technical data:
The first app is free (and no advertisements!!!), it's called "Unpopular Music Player":
A description why I wrote the program can be found here:
Additionally, the Play Store entry includes a detailed description.
The second (larger) app is called "Opus 1 Music Player":
Development of that one took a long time and much effort, because of the sophisticated filter functions. Thus I tried to offer it for a minimal price. The full functionality is described in the Play Store entry. So far I did not find a program with similar functionality.
I hope that my apps are useful for more people than just for me, and, I remind: Ask for a voucher if you want to have the "Opus 1" program as gift or present!!!
PS: The Unpopular Music Player is available since Feb 2016, the Opus 1 Player since October of the same year.
PS/2: I paid 25 USD to Google just to upload a free program!