Still, streaming platforms provide opportunities.

Zhang's team found about 1.3 billion of the roughly 5 billion yuan in China's documentary investment came from online platforms, a more than 18 percent year-on-year increase.

Youku produced a total of 260 hours of original documentaries. Tencent made about 23 titles. And these account for about a third of their total productions uploaded last year.

"No matter how storytelling methods evolve, documentaries always deal with what is changing in our lives and what remains unchanged," says Youku's vice-president and chief supervisor of documentaries, Gan Chao.

"But formats can be creative."

Food remains the most popular Chinese online-documentary topic, research finds.

Some acclaimed productions like Flavorful Origins have been introduced to global platforms like Netflix.

Peking University media professor Lu Di says Chinese producers should look beyond stereotypical and established topics, even though these are often pathfinders for international markets.

"It's better to not rest on laurels," Lu says.

"But today's Chinese documentaries that are broadcast overseas are still dominated by the Forbidden City, the Great Wall, natural scenery and food. We can't only look for short-term returns."

Zhang also believes overemphasis on global cooperation in documentary production today may relegate some pressing social topics.