This endpoint returns all movies (including duplicates):
/emby/Items?api_key={apikey}&Recursive=true&IncludeItemTypes=Movie&Fields=Path,TagLines,Overview,PremiereDate,Genres,MediaStreams&SortBy=Name&SortOrder=Ascending
This endpoint returns all movies (excluding duplicates):
/emby/Users/{userid}/Items?api_key={apikey}&Recursive=true&IncludeItemTypes=Movie&Fields=Path,TagLines,Overview,PremiereDate,Genres,MediaStreams&SortBy=Name&SortOrder