Plex is entirely legal, free, and available directly on the official PlayStation Store. Instead of forcing the PS4 to decode heavy files, Plex uses your home computer or a dedicated server to do the heavy lifting.
Sony's PlayStation 4 is a closed platform. Its security measures restrict software installation to only encrypted, digitally signed packages downloaded directly from the PlayStation Network (PSN). These official PKG files are cryptographically tied to a specific console and PSN account. vlc ps4 pkg