This can be seen in Welles' version of Macbeth (1948).
MacBeth declares "We have scorched the snake, not killed it" (MacBeth 2005, 00:41:06-00:41:08)...
Note: after the first mention in your writing you can just use the film title.
Title, Year [material designation]. Subsidiary originator (if applicable e.g. Director). Production details
Macbeth, 1948 [film]. Directed by Orson WELLES. USA: Republic Pictures
If you are referring to a particular scene or quote, you should include in the citation the times (hours, minutes and seconds) between which it takes place in the film. See example above.