In a briefing to the Government in June, the Treasury said the $55 million figure was based on the assumption that the costs to these sectors would be similar to the cost for books and music.
Officials were also unable to quantify the impact of a longer copyright term on "derivative works" - the re-use of original works by creative industries.
"As a result, uncertainty remains about the total eco-nomic cost of copyright concessions," the report said. "If anything, we think these figures are likely to represent an underestimation ..."
The document said the higher costs could be offset by a gradual phase-in of the longer copyright period.
InternetNZ work programme director Andrew Cushen said the change meant increased costs for New Zealanders, and greater revenue for overseas copyright holders.
"We will pay more over time to access music and movies. We will also pay more over time for books and educational resources, making it more expensive for us to learn and to do business."
Mr Cushen said the $55 million did not take into account the increased cost and difficulty of re-using copyright works.
New Zealand musicians, authors, film-makers and artists will benefit from the longer copyright term, though MFAT says these benefits will be modest. For example, pop star Lorde will now be able to claim royalties for her original works until she is in her 80s, instead of into her 60s.
Labour leader Andrew Little said the documents showed the benefits of the TPP were less certain than the Government had made out.
Added costs
• Copyright term to be extended from 50 years to 70 years under the TPP.
• For literary works, the 70-year term begins when the author dies.
• For film, television and music, the 70-year term begins when the work is released.
• Estimated cost to consumers of at least $55 million a year in the long-term.
