Stephan Komandarev's latest film started as a joke.

"I was in a taxi talking to the driver when he asked me, 'Do you know why Bulgaria is the Land of Optimists?'" said Komandarev, who still laughs at the idea.

"It's the Land of Optimists because all the pessimists and the realists have already left," the driver told him.

That bitter joke set the film-maker, the first Bulgarian ever to be shortlisted for the Oscars, thinking.

The Balkan country has lost a fifth or more of its population since the fall of Communism despite becoming a member the EU a decade ago.

"There were nine million of us when the wall came down, and we are now around five million. And there hasn't been a war," the director told AFP. 

Official figures put Bulgaria's population closer to seven million -- statistics Komandarev says are contested, claiming they do not take into account millions of Bulgarians who spend most of the year working abroad.

Whatever the figure, experts agree Bulgaria's population is likely to become the fastest-shrinking in the world.

- Taxi driver priests -

So Komandarev set out to make a kind of "Canterbury Tales" of the disappearing Bulgarians told through the taxi drivers of the capital Sofia and their passengers.

Over the course of a day and a night, "Directions" -- or "Taxi Sofia" as it is called in some countries --  follows teachers, businessmen and even a priest driving taxis to make ends meet. 

"There are three priests driving taxis right now in Sofia," said Komandarev.

"Anyone who has lost their job or who is paid very little, like school teachers and academics, drive taxis at night. These people see real life on the streets, not just the life we see on television."

The taxi driver who told Komandarev the joke was a professor of nuclear physics at the country's Academy of Sciences until he lost his job during the "interminable transition" to the market economy, which has already lasted 27 years in Bulgaria.

"We have been waiting for what seems like several lifetimes for the invisible hand of the market to sort everything out," said the director, who had an international hit with his upbeat "The World is Big and Salvation Lurks Around the Corner".

"In the meantime, we have lost our social system and education system. I am not nostalgic for Communism -- I was so happy when it ended -- but we destroyed things that we should have kept," Komandarev argued.

He said the EU's poorest state had "gone from for totalitarianism to extreme capitalism. 

"The impression you get from the media is that everything is going great. 'We are in the EU!' But the reality is people are getting poorer, the level of education is falling and old people are living in a terrible way," he said.

- 'Permanent ex-Communist' elite -

Komandarev insists his film's portrait of the travails of "transition" holds true not just for Bulgaria but for several Eastern Europe countries.

The film bible Variety hailed it as a "clever, fleet-footed" snapshot of Bulgarians left behind, and praised its "poignant accuracy and flashes of wry humour", comparing its favourably with Jim Jarmusch's "Night on Earth".

It is not the first time the director has taken on his country's woes. He tackled the rural exodus in his 2010 documentary "The Town of the Badante Women" about a community whose women had all left for Italy to look after old people there.

His last feature, "Judgment" took on the prickly subject of the migrant crisis from the point of view of a former border guard who ends up smuggling Syrian refugees over the frontier from Turkey on which Bulgaria has now built a fence.

With such engagement, Komandarev, 51, admits that he has come under pressure to enter politics himself.

"I have been asked several times but I have always refused. My films are my strength. Ten years ago I was a lot more optimistic than I am now."

And Komandarev is despairing of what he calls a "real lack of renewal" at the top. 

"Those who formed the Communist elite," he said, "are still in power or their families hold great economic power. They have done a 180-degree switch, and now they are for the market. 

"But it is the same people..."