Blog post: http://adelnizamutdinov.github.io/blog/2015/01/23/using-rxjavas-observable-semantics-for-greater-good/

RxMediaPlayer.java

import android.media.AudioManager;
import android.media.MediaPlayer;
import android.util.Pair;
import org.jetbrains.annotations.NotNull;
import java.io.File;
import java.io.IOException;
import java.util.concurrent.TimeUnit;
import rx.Observable;
import rx.subscriptions.Subscriptions;

public class RxMediaPlayer {
    public static @NotNull Observable<MediaPlayer> from(@NotNull File file) {
        return Observable.create(subscriber -> {
            final MediaPlayer player = create();
            try {
                player.setDataSource(file.getAbsolutePath());
                subscriber.onNext(player);
                subscriber.onCompleted();
            } catch (IOException e) {
                subscriber.onError(e);
            }
        });
    }

    public static @NotNull Observable<Pair<Integer, Integer>> play(@NotNull MediaPlayer mp) {
        return prepare(mp).flatMap(RxMediaPlayer::stream);
    }

    static @NotNull MediaPlayer create() {
        final MediaPlayer player = new MediaPlayer();
        player.setAudioStreamType(AudioManager.STREAM_MUSIC);
        return player;
    }

    static @NotNull Observable<MediaPlayer> prepare(@NotNull MediaPlayer mp) {
        return Observable.create(subscriber -> {
            try {
                mp.prepare();
                subscriber.onNext(mp);
                subscriber.onCompleted();
            } catch (IOException e) {
                mp.reset();
                mp.release();
                subscriber.onError(e);
            }
        });
    }

    static @NotNull Observable<Pair<Integer, Integer>> stream(@NotNull MediaPlayer mp) {
        return Observable.create(subscriber -> {
            subscriber.add(Subscriptions.create(() -> {
                if (mp.isPlaying()) {
                    mp.stop();
                }
                mp.reset();
                mp.release();
            }));
            mp.start();
            subscriber.add(ticks(mp)
                                   .takeUntil(complete(mp))
                                   .subscribe(subscriber));
        });
    }

    static @NotNull Observable<Pair<Integer, Integer>> ticks(@NotNull MediaPlayer mp) {
        return Observable.interval(16, TimeUnit.MILLISECONDS)
                .map(y -> Pair.create(mp.getCurrentPosition(), mp.getDuration()));
    }

    static @NotNull Observable<MediaPlayer> complete(@NotNull MediaPlayer player) {
        return Observable.create(subscriber -> player.setOnCompletionListener(mp -> {
            subscriber.onNext(mp);
            subscriber.onCompleted();
        }));
    }
}