PixelDroid-App-Android/app/src/main/res/drawable/play_pause.xml

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item
        android:drawable="@drawable/play"
        android:state_selected="true" />
    <item
        android:drawable="@drawable/pause"/>
</selector>