Plex Documentation → Scanners & Agents
→ Advanced Settings Plex Movie Agent
→ Advanced Settings Plex TV Series Agent
Plex Documentation → Libraries
→ Editing Libraries
Plex will read embedded metadata from mp4 files if configured to do so.
However, the setting @anon5074910 mentions, which enables the capability, is off by default. Edit the library to enable the capability.
If Plex does not do so automatically, refresh the library metadata after changing the setting.
See the documentation linked above for additional details.
I believe Plex will read the IMDB ID from a .nfo file. It will not read any other metadata from such a file.
