Plex has spent the last year building new software for the living room PC “from the ground up”. The old Plex Home Theater is being replaced with the new Plex Media Player that has an updated user interface, new features, and native support for 4K.
Plex Media Player
Some of you already know and use Plex but for those of you unfamiliar with it think of it as software for watching/listening to your locally-stored media files, such as video, movies and music, on the living room TV screen over WiFi. This version is for a PC/HTPC placed in the living room.

Plex says that they have built the new software for the living room PC from scratch. It no runs on the foundation of Kodi/XBMC but is instead powered by open-source mpv, which Plex believes has better support for media files. Plex promises that it can play virtually any video, music or photo format that you throw at it.
The new “Plex Media Player” replaces the old “Plex Home Theater”, which you can continue but which will no longer see significant updates. The most apparent change is the new graphical user interface that now looks like Plex clients on Smart TVs and media streamer boxes.

With the new software Plex is also adding native support for 4K video and the HEVC format. Other new features include a 4K user interface, mouse controls, multi-channel music support, a native Raspberry Pi port, and more granular audio delay settings.
However, some features have yet to be added, including search, video playlists and Cloud Sync integration. Those will be added in the near future.

Plex Media Player is only available for Plex Pass subscribers right now. It will be available to everyone for free later. Plex also recently updated its Smart TV app and went free on Roku and Xbox 360.
New features in Plex Media Player
The best-in-class mpv engine is used for playback |
Improved video codec support (e.g. H.265) |
A true 4K interface |
Bit-perfect LPCM decoding of DTS-HD MA (using libdcadec) |
Shared code-base with many of our other apps (including PlayStation, Smart TVs, and Xbox One), allowing faster development |
Streamlined interface that brings our premium desktop app in line with the rest of our big screen offerings |
Snappier and more feature-rich UI, including better animations |
Support for multi-channel music tracks |
Allows for different audio delay depending on video framerate (23.976 Hz vs. the rest) |
Native Raspberry Pi 2 port |
Mouse support |