Question: Which film director also appeared on screen as an actor, Dziga Vertov or Frederic Zelnik?

Context paragraphs:
Frederic Zelnik: Frederic Zelnik (17 May 1885 - 29 November 1950) was one of the most important producers-directors of the German silent cinema.  He also appeared on screen as an actor.

Jo Bole So Nihaal (film): Jo Bole So Nihaal (also transliterated as "Jo Bole So Nihal"; literally meaning "Whoever utters shall be fulfilled") is a 2005 Bollywood action comedy film, directed by Rahul Rawail.  It stars Sunny Deol, Shillpi Sharma and Kamaal Khan in lead roles, whilst Nupur Mehta and Surekha Sikri appear in major supporting roles; the director also plays an antagonistic role in the film.  Singer Kamaal Khan appeared first time on big screen in a negative role.  This movie was his debut movie as actor.

Cinema of Ukraine: Ukraine has had an influence on the history of the cinema.  Prominent Ukrainian directors include Oleksandr Dovzhenko, Dzyha Vertov and Serhiy Paradzhanov.  Dovzhenko is often cited as one of the most important early Soviet filmmakers, as well as being a pioneer of Soviet montage theory and founding Dovzhenko Film Studios.  In 1927 Dziga Vertov moved from Moscow to Ukraine.  At the film studio VUFKU he made several avant-garde documentaries, among them «The Eleventh Year», «Man with a Movie Camera» and first Ukrainian documentary sound film «Enthusiasm (Symphony of the Donbass)».  Paradzhanov was an Armenian film director and artist who made significant contributions to Ukrainian, Armenian and Georgian cinema; he invented his own cinematic style, Ukrainian poetic cinema, which was totally out of step with the guiding principles of socialist realism.

Kino-Eye: Kino-Eye (Anglophonic: Cine-Eye) is a film technique developed in Soviet Russia by Dziga Vertov.  It was also the name of the movement and group that was defined by this technique.  Kino-Eye was Vertov's means of capturing what he believed to be "inaccessible to the human eye"; that is, Kino-Eye films would not attempt to imitate how the human eye saw things.  Rather, by assembling film fragments and editing them together in a form of montage, Kino-Eye hoped to activate a new type of perception by creating "a new filmic, i.e., media shaped, reality and a message or an illusion of a message - a semantic field."  Distinct from narrative entertainment cinema forms or otherwise "acted" films, Kino-Eye sought to capture "life unawares" and edit it together in such a way that it would form a new, previously unseen truth.

Southern Roses: Southern Roses is a 1936 British musical comedy film directed by Frederic Zelnik and starring George Robey, Gina Malo and Chili Bouchier.  It was shot at Denham Studios.  The film's sets were designed by the art director Frederick Pusey.

Enthusiasm (film): Enthusiasm: The Symphony of Donbass [Russian: Энтузиазм: Симфония Донбасса or Entuziazm: Simfoniya Donbassa], also referred to as "Enthusiasm", "Donbass Symphony", or "The Symphony of the Donbas Basin".  "Enthusiasm" is a 1930 Soviet sound film, directed by Dziga Vertov.  Although "Enthusiasm" is not one of Vertov's more popular films, such as Man with a Movie Camera, the film was the director's first sound film and also the first sound film of the Soviet production company Ukrainfilm.  The film is also notable for the fact that it is a documentary filmed on location.  Like many of his other films, Vertov worked on "Enthusiasm" with his wife Elizaveta Svilova.

Fabio Garriba: Born in Soave, Garriba started his career on stage, and in 1969 he made his film debut in Dziga Vertov Group's "Le Vent d'est".  He later worked with prominent directors such as Roberto Rossellini, Bernardo Bertolucci, Ettore Scola, Marco Bellocchio and Luigi Magni.  He also had leading roles in films directed by his twin brother Mario, notably the Golden Leopard winner "On the Point of Death".

Collective for Living Cinema: The Collective for Living Cinema was an outpost of avant-garde cinema located on White Street in Lower Manhattan in the United States of America.  It regularly presented work by filmmakers such as Ken Jacobs, Johan van der Keuken, Yvonne Rainer, Christine Vachon, Dziga Vertov and many others who created films that were outside of the commercial mainstream in the United States.  It also published a number of scholarly journals on film.  Many of the founders studied film at Binghamton University together, where they developed a particular interest in the avant-garde.

The Green Manuela: The Green Manuela (German: Die grüne Manuela) is a 1923 German silent drama film directed by Ewald André Dupont and starring Lucie Labass, Josef Winter and Grete Berger.  The film is based on a novel by Clara Ratzka.  A gypsy dancer becomes involved with some smugglers in Spain.  The film's plot bears a number of similarities to "Carmen".  It was the first time Dupont worked with the cinematographer Werner Brandes and the art director Alfred Junge who were to become important collaborators with him.  The poster of this movie is seen in Russian director Dziga Vertov's movie Man with a Movie Camera (1929) playing at a theater named the Proletarian.  It's a symbol of Vertov's disdain of Western fanciful films.

Dziga Vertov: Dziga Vertov (Russian: Дзига Вертов ; born David Abelevich Kaufman, Russian: Дави́д А́белевич Ка́уфман , and also known as Denis Kaufman; 2 January 1896 – 12 February 1954) was a Soviet pioneer documentary film and newsreel director, as well as a cinema theorist.  His filming practices and theories influenced the cinéma vérité style of documentary movie-making and the Dziga Vertov Group, a radical film-making cooperative which was active from 1968 to 1972.

Supporting paragraphs: Dziga Vertov Frederic Zelnik
Answer: Frederic Zelnik