Android

Android is an open platform.

It is a very popular platform to drive smart phones.

As this website is about file based audio, I will focus on the audio part.

USB audio

Voices on the internet says that Android supports USB audio.

Others say it don't.

Android 4 introduced accessory mode. It expect a host and most DAC's are not a host.

Android 5 supports USB audio in host mode.

More details can be found here.

Native sample rate

Most phones have a fixed native sample rate of 48 kHz.

This means all audio had to be resampled to this rate for local playback.

Note that this is a property of the phone, not a limitation inherent to Android.

AudioFlinger

Android has a native audio system called AudioFlinger.
It provides an API for playback/recording

Multiple values

Often in tags like Artist you have often more than one performer.
Once I asked the developer of UPnPlay why this was not supported in his app.
According to him the data mode of the Android Mediastore simply don’t support this.

References
  1. USB audio - Android Open Source Project
  2. PulseAudio vs. AudioFlinger - Arun Raghavan