Australia's memory institutions are racing to digitise their magnetic tape collections before the year 2025, when archivists around the world expect it will become almost impossible to find working tape playback machines.

Key points: 130,000 hours of audio and video held on magnetic tape by the National Archives

130,000 hours of audio and video held on magnetic tape by the National Archives Machines need to play and digitise the tapes are expected to disappear by 2025

Machines need to play and digitise the tapes are expected to disappear by 2025 The National Archives has been scouring eBay and Gumtree to find suitable machines

The National Archives of Australia holds some 130,000 hours of audio and video tape that still need to be rescued.

"We have this incredible, vast expanse of recorded memory of Australia from the 20th century and all of it, now, is at risk — through technological obsolescence — of being lost altogether," National Archives director general David Fricker told 7.30.

While no-one knows exactly what the remaining tapes contain, the ones that have already been converted give a good sample of the rich history at risk.

They contain fascinating evidence of the actions of Australian government agencies in the past — including CSIRO experiments, nuclear tests at Maralinga, ASIO surveillance vision, audio logs recorded by special forces soldiers in World War II and rare audio tapes of Indigenous languages.

The tape problem

Old recording equipment at the National Archives. ( ABC News )

Magnetic tape is different to film, which is a fundamentally simple technology. Shine a light through film, and you can see the picture.

Tapes, on the other hand, can only be read by format-specific machines.

And dozens of formats of magnetic tape were created through the last century — one-inch, two-inch, various versions of Betamax.

"By nature of the equipment we're dealing with, most of it is old and obsolete and hasn't been manufactured for decades," said Jason Crowe, manager of audio-visual preservation at the Archives.

The key component in each machine, the magnetic head, has a finite life.

"Each head only has a certain number of hours it is capable of working for before it peaks out and needs replacement," Mr Ficker said.

For most machines that is around 5,500 hours, according to Mr Crowe.

Even the more recent formats are now obsolete.

Magnetic tapes waiting to be digitised. ( ABC News )

In 2016 Sony announced it would stop making Betamax tapes. The ABC has years of newsreel and other programs stored on Betamax tapes, and is working closely with the Archives to save as much as possible.

Many institutions copied their film collections on to tape thinking it would be more future-proof. It turns out they would have been better off leaving it on film.

The Archives is using its limited budget to pick up tape machines wherever it can find them.

Archivists scour online marketplaces like eBay and Gumtree looking for machines for sale, even broken machines that can be harvested for working parts.

And it's not just the machines that are on their way out.

"As the technology has changed, people are no longer learning how to use the older machines," Mr Crowe said.

"It's mostly ex-industry people, working for the preservation service."

'Unseen evidence'

Footage of Prime Minister Harold Holt spearfishing is part of the National Archives collection. ( Supplied: National Archives )

While the National Film and Sound Archive is more focused on Australia's cultural history, the job of the National Archives is to preserve the history of the Australian government.

"The job of the Archives is not to keep this stuff because it's pretty or because it has commercial potential," Mr Fricker said.

"We're keeping these records because they matter. They affect the rights and entitlements of Australians.

"They are perhaps unseen evidence of government decisions and government activities in the past."

A former ASIO officer, Mr Fricker said the ASIO surveillance tapes in the Archives' collection played a vital role in maintaining public faith in Australia's intelligence agencies.

National Archives Director General David Fricker says making archives available can help counter conspiracy theories. ( ABC News )

"Organisations like ASIO ... have to operate in secret to be effective," he said.

"Australia needs a security service which can operate. But with the passage of time Australians need to know, well, has our security service behaved itself properly?

"How do we stop conspiracy theories spreading far and wide about what we did or didn't do?

"And the answer is because after the passage of time, through the work that we do at the Archives in conjunction with ASIO, we can release those records to the public."

There are also tapes of Indigenous Australians telling stories, sometimes in Indigenous languages now at risk of being lost.

Mr Fricker says there are many such cases where tapes that were taken for purely functional reasons at the time, later become objects of academic research for entirely different reasons.

"It is absolutely essential that we don't lose them, because when these are lost they can't be reconstructed. They can't be recreated," he said.

"They will be erased from Australia's memory and it would be a real tragedy if that were to occur."

Can't we just build more machines?

An old tape player used by the National Archives to help digitise video and audio. ( ABC News )

In the age of the 4K smart TV, audio-visual companies are looking forward to ever-greater digital innovations. Few are looking back at the cavalcade of tape formats that came before, which never had the same desirable aesthetic that made film so enduringly popular.

Mr Ficker says it is "very unlikely" that archives around the world could raise the capital to have tape machines manufactured again, even if they worked together.

But he said he "hadn't written it off", because "if that's what it takes, will then we will be pursuing those strategies".

He also suggests future digital innovations might make it possible to read the data off magnetic tapes in a different way, using software to reconstruct the images.