Thanks to the following open source libraries.
google/ExoPlayer Apache License 2.0
https://github.com/google/ExoPlayer/blob/r2.8.2/LICENSE
square/picasso Apache License 2.0
Copyright 2013 Square, Inc.
https://github.com/square/picasso/blob/master/LICENSE.txt
daimajia/AndroidImageSlider MIT
https://github.com/daimajia/AndroidImageSlider/blob/master/LICENSE
NanoHttpd/nanohttpd BSD 3-Clause "New" or "Revised" License
Copyright (c) 2012-2013 by Paul S. Hawke, 2001,2005-2013 by Jarno Elonen, 2010 by Konstantinos Togias All rights reserved.
https://github.com/NanoHttpd/nanohttpd/blob/master/LICENSE.md
yydcdut/SlideAndDragListView Apache License 2.0
Copyright 2015 yydcdut
https://github.com/yydcdut/SlideAndDragListView/blob/master/LICENSE
This module is not used since v3.9.3
zxing/zxing Apache License 2.0
Copyright 2008 ZXing authors
https://github.com/zxing/zxing/blob/master/LICENSE
Creativity103.com Creative Commons Attribution 3.0 License
The following picture is used as the wallpaper of Audio Player.
http://creativity103.com/collections/Lightwaves/slides/pastel_light_lines.html
License: https://creativecommons.org/licenses/by/3.0/