LAGOS — By his own estimates, Lancelot Oduwa Imasuen has directed somewhere between 150 and 200 movies over the course of his 20-year career — including hits like “Games Women Play,” “Last Burial” and “Behind Closed Doors,” which have made him one of the most prolific directors in the Nigerian film industry, popularly known as Nollywood.

But Imasuen tends to distance himself from his early, mercenary years, when producers would approach him with shoestring budgets and shoddy scripts for movies he might have shot in just four days. Today he produces and directs his own films. “I wouldn’t even have the time to be as prolific as I used to be,” he said recently, while discussing his latest movie, “Invasion 1897.”

An epic tale about the British Army’s ransacking of the ancient West African kingdom of Benin, “Invasion” was a labor of love that took Imasuen close to four years to produce. Ten years ago, the movie’s million-dollar budget would have been enough to make a movie like “Games Women Play” and 24 sequels. But like many of his peers, who have watched shrinking investments and rampant piracy hobble their industry, Imasuen is gambling that big-budget, big-screen blockbusters will breathe fresh life into Nollywood.

“If ‘Invasion’ can make back its money, then rest assured that production is going to come up in Nigeria,” he said with characteristic swagger.

It is an uncertain time for Nollywood, the homegrown movie industry whose baroque tales of fast money, gunplay, witchcraft and amorous treachery have captivated audiences for more than two decades. Once a fledgling film biz built around low-budget home movies sold on VHS tapes, the industry has grown into a $5 billion juggernaut, which UNESCO credited in a 2006 study as being the second-most prolific movie industry on the planet, ahead of Hollywood and behind only India’s Bollywood.

But since then, the numbers have been in steady decline, according to Don Nkems, of the Association of Nollywood Core Producers (ANCOP), which estimates that the industry’s production peaked at more than 2,600 films in 2008. Even UNESCO, in its most recent report on the global film business, criticized the industry’s “semi-professional/informal productions” as it downgraded Nollywood’s output. In the U.N. agency’s roundup of the most prolific film industries on the planet, Nigeria didn’t even crack the top 10 list.