Here is a short article I wrote to share my experience using Samsung Link to share multimedia content between devices on a Wi-Fi network. After trying out Samsung Link and exploring the possibilities, imo it integrates a lot of very nice features together in an easy to use way. Apart from streaming/playback of audio/video/pictures, it is also a great way to transfer ANY file on your S4 over Wi-Fi to a PC or vice versa:
Samsung Link: Sharing Multimedia Content
Samsung Link: Sharing Multimedia Content