The international investigative judge for the court told VOA Khmer he anticipates at least two years of proceedings.
Members of the CPP have ignored a court summons for testimony from the former international investigative judge.
Thet Sambath said aspiring filmmakers who wish to do similar projects must be ready to work hard.
Some regime leaders have said in the past they had hoped to protect the country from Vietnamese occupation and others.
Victims from the Trapaing Thmar dam project say they want the judges to investigate closely Case 004.
Pen Sovann said the Khmer Rouge left him with “no choice” but to set up a movement to oppose them in the 1980s.
The extra hearing will be held just one month before the trial is scheduled to begin in September.
The UN-backed tribunal has come under increased pressure in recent months, after investigating judges concluded their work in Case 003.
The Documentation Center of Cambodia has distributed more than 400,000 copies to high schools across the country.
The tribunal has spent around $150 million since 2003, and began operation in 2006.
Court officials have denied any political influence in cases 003 and 004.
Former leaders Noun Chea, Khieu Samphan, Ieng Sary and Ieng Thirith have all denied atrocity charges.