see above… if you use mp4/m4v files, you can edit the embedded metadata and enable it in plex (using local media assets and/or enabling embedded metadata).
if you have the data in a supported format, you could use a respective agent… this post started ages ago – you might need to check if the plugin is still up-to-date / working:
edit: personally I would embed the metadata right in the video files. this way nothing gets lost if (god forbid) your library gets corrupted and you need to re-load it from scratch.
