Plex is a free media server add-on for many devices, including Chromecast, Xbox, Playstation, Apple devices, Roku, Fire TV, and more.
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Pros
Pro Supported on many devices
It's pretty hard to find a NAS or STB that doesn't support Plex.
Pro Accessible via web browser
A modern web browser is enough to get everything Plex has to offer.
Pro Added lots of media databases
Metadata for media files will automatically be updated by using media databases. This provides posters, movie trailers, descriptions, information about actors, etc.
Cons
Con Needs registration
You need a PLEX account even if you use it on your local LAN.
Con Proprietary software
Unfree software.
Con No gapless audio-playback
Plex still does not support gapless playback of audio files such as mp3 or FLAC.
Con Playback error: This server is not powerful enough to convert video
More hardware requirements on Plex due to a useless/non-intuitive transcoder. When using lower spec hardware (eg SBC) Plex will not transcode or play HD+ videos. When compared to other packages (eg Jellyfin which transcodes nicely using FFMeg), Plex falls short on video playback and transcode settings to get videos to play (fastest/lightest option still fails).