A biting winter wind sends little snowflakes dancing along a stretch of the Spree River in Berlin. Director Claus Clausen stands armed with thick boots and a fur-trimmed parka by a cameraman to whom he gives quiet instructions. Despite the icy weather, the mood is upbeat but concentrated. The protagonist Ai Lao, age six, is wrapped up warmly and waiting for his part.

The ambitious project, titled "Berlin, I Love You," has been allotted just three days of filming. Cameraman Frank Griebe is an experienced pro. He worked under director Tom Tykwer on major film projects such as "Lola rennt" (Run Lola Run), "Das Parfum" and "Cloud Atlas."

Griebe now has an unusually talented performer in front of the camera: Ai Lao, Ai Weiwei's son, isn't put on edge by the large film crew. He's been living for the last six months with his mother Wang Fen in Berlin. His cousin is also on the set, so that Ai doesn't get bored surrounded by all the grown-ups.

Ai Lao shows impressive assuredness once on camera, riding a bike - a brand new skill for him - along a riverbank void of people. Behind him are the outlines of the German parliamentary building and the Chancellery. It's a child in the shadows of power, a typical image for Ai Weiwei.

Directing via Skype

Using Skype, the Chinese artist can meticulously follow the shoot from his studio. Director Claus Clausen translates the directions from Beijing in a short and snappy way on set in Berlin. Before each take, he shows Ai Weiwei the scenery at hand again with his smart phone. The two discussed everything in detail beforehand, and Clausen was also the one who had the idea for this unusual approach.

The film isn't a political statement. It's a poetic art piece about the difficult long-distance relationship between the small Ai Lao, who now lives in Germany rather than in China, and his famous father. Since the summer of 2014, the two can only see each other via Skype - a fact that often saddens the artist's son.

Scenes in which he doesn't want to talk on the phone with his father are among the very private stories told in the film.

The shoot is taking place in three places where the former border between East and West Berlin can still be detected. Small bronze plates on the ground show visitors where the border was. For the first day of filming, the team set up its tents at the futuristic Crown Prince Bridge, which was built in 1991-92 to bridge east and west. The third day sees filming at a piece of the wall still standing in northern central Berlin.

The setting reflects the theme of the film, director Clausen tells DW: "It's about the divided city, long-distance relationships, families that were torn apart. So, you need a director who is involved with the city."

Ai Weiwei has long had artistic connections with Berlin. While he was in prison in Beijing in 2011, he was made an honorary member of the Berlin Academy of the Arts, a sign of cultural solidarity from Germany. He became a guest professor at Berlin's University of the Arts in 2014, and he holds his lectures via Skype - just as he communicates now with his team during filming. Edda Reiser, co-producer of "Berlin, I Love You," says the short film does have a political dimension: "We want to use this project to show that film can overcome all boundaries. And that a free heart cannot be caged."

Crossing boundaries

Meanwhile, a child double is being substituted in for Ai Lao. The icy wind is leaving everyone cold to the core. His mother wraps him in a down jacket and a thick wool blanket after each scene, and a limousine serves as a warm-up station for the family.

Director Clausen makes good headway, though. The Skype connection with Beijing functions perfectly, and the scenes come together with speed. The film team's next stop is at the famous Checkpoint Charlie in central Berlin.

"Little Ai Lao is such a talent and not shy," says Clausen, satisfied. "You couldn't ask for better."

Documentary filmmaker Wang Fen wrote the script for this biographical short film. Ai Weiwei studied in 1978 at Beijing's film academy under famous Chinese directors such as Zhang Yimou ("Raise the Red Lantern," "House of the Flying Daggers"), but the artist rarely uses film as a mode of expression. He tends to cross the boundaries between conceptual art, painting and sculpture.

But the Berlin film immediately piqued his interest, Claus Clausen says: "In many cities, there's this polarity between beauty and ugliness, between culture and kitsch, between commerce and art. But in Berlin, that all exists side by side and serves as mutual inspiration."

Hoping to be in Berlin

The short film Ai Weiwei is overseeing is the first part of the film tableau "Berlin, I Love You," which will be completed over the course of the year. Amid the Berlinale crowds, viewers can watch the current footage at Potsdamer Platz in Berlin. This sort of transparency is part of Ai Weiwei's artistic concept.

"In September and October of 2015, we want to start the principal shoot with 10 other directors," Clausen says. "Many of them are bringing their own scripts."

"Berlin, I Love You" is the latest in a series that includes "Paris, je t'aime" (2006), "New York, I Love You" (2009) and "Rio, Eu Te Amo" (2014), which have all already been in theaters. The new installment will likely have its premiere at next year's Berlinale.

Ai Weiwei tells journalists via Skype that he hopes he will have his passport back by then and can be on hand for the premiere.