It took so long for Annie Sundberg and Ricki Stern to make their first big-screen documentary that the technology they started with was superseded.
The New York film-makers, whose previous projects had focused on the hardscrabble lives of black kids in Harlem, had taken an interest in the case of Darryl Hunt, a young black man in North Carolina whose conviction for the rape and murder of a young white journalist looked more than a little unsafe.
The 1984 conviction, by a jury of 11 whites and one black and based largely on the testimony of an avowed Ku Klux Klansman, had put Hunt in jail for 10 years by the time a college friend of Stern's, working on Hunt's defence team, told her about an imminent test of DNA collected at the crime scene.
"This was possibly the first DNA exoneration in the US," recalls Stern, "and we were thinking, wow, we could get this on film."
They got it on film all right: the judge said although the DNA was certainly not Hunt's, it did not conclusively clear him of involvement in the murder.
This guilty-until-proven-innocent Southern justice - which would, incredibly, be confirmed by that state's appeal court and the US Supreme Court - horrified the two northerners, but they had to accept that the case was closed.
"We returned to New York and the film shot that day was put into storage in a domestic freezer where it remained, exposed but not processed, never seen for 10 years," says Sundberg.
But in 2003, they learned of a dramatic development that meant Hunt might be released from prison. They were back shooting - but this time the medium was digital video. Meanwhile, they recovered the film from the freezer and sent it for processing, hoping that the images were okay.
Fortunately, time had been kind to the film on ice; the new and old images work well side by side and The Trials of Darryl Hunt is one of the most potent and dramatic of an excellent selection of documentaries in the International Film Festival, which starts next week.
In fact, the film is one of two documentaries by the pair on this year's programme.
The Devil Came on Horseback uses exclusive photographs of the genocide in Darfur taken by former US Marine Captain Brian Steidle during his role as a military observer with the African Union.
Though undeniably grim in parts, it is ultimately an uplifting film about one man's determination to ensure that Darfur did not, like Rwanda, become another ignored war.
By contrast with the Darryl Hunt film, 13 years in the making, Devil "came upon us quickly and urgently", says Sundberg. But generally speaking, the process of documentary film-making is the practice of patience.
"I don't know if we could have done Darryl Hunt now," says Stern.
"We took a great risk. If you go to film festivals and see all these great documentaries, these are heart-and-soul projects in which people went out on limbs to seek a story.
"A lot of these are part-time film-makers who just jumped off the edge and went for it.
"They didn't know how they would get it finished. They didn't know if they were going to get funding."
Sundberg notes that the budgets for these films - typically less than US$500,000 ($640,000) which is around what a Hollywood feature spends on limousines - are always easy to raise when you don't need to raise them.
"One of the ironies is how hard it is to get money when you need it, when you are just starting production and just starting to shoot.
"When you have developed some critical mass and you've got some sort of rough cut, it's amazing how people want to give you money - basically when you have already climbed up the mountain."
The past decade of documentary film-making, often dubbed a new golden age, has seen the simultaneous development of two trends: the unabashedly polemical film - the work of Michael Moore might be seen as the most extreme example - and the narratively dramatic, where the style is indistinguishable from fiction features.
Sundberg says that Whale Rider had elements of documentary, of living inside another culture.
"The forms - dramatic and documentary - aren't that far apart. In the end, it's about working to get to the truth of an experience, of a character, and that's what keeps you engaged.
"The value of pure joyous entertainment cannot be underestimated in this day and age," adds Stern.
"People are tired of tackling issues, they are afraid and exhausted.
"But people are enjoying documentaries because increasingly they are so well made and they are dramatic and told in narrative ways and people can watch them as if they are fiction pieces."
What: The Telecom 39th Auckland International Film Festival
When: July 13 to July 29
Where: The Civic, SkyCity cinemas Queen St, SkyCity Theatre, Academy Cinema
Tickets: Available now from Ticketek and Civic box office.