Drone currently uses the file name, looking for source (HDTV, WEBDL, etc) and resolution (720p, 1080p, etc), failing to find those, it would use the extension to determine the quality, since mp4 is most often associated with SDTV x264 it would treat it as SDTV.
Examples:
The.Series.S01E01.720p.WEBDL = WEBDL 720p
The.Series.S01E01.HDTV = SDTV
The Series - S01E01.mkv = HDTV 720p
The Series - S01E01.avi = SDTV