Formal:
* Solo film: This term emphasizes the single individual's role in both writing and directing.
* Single-person film: Similar to "solo film," it clearly indicates one person was responsible for both aspects.
Informal:
* Auteur film: This term implies a strong personal vision and artistic control by the filmmaker, though not necessarily solely written and directed.
* One-man show: This casual term emphasizes the single individual's responsibility for the entire film.
* Self-written and directed: This straightforward description explicitly states the filmmaker's dual roles.
Other options:
* You can also simply say "written and directed by [name]" to be clear and concise.
Ultimately, the best term to use depends on the context and the desired level of formality.