A newly engaged NSW couple who plunged from a cruise ship, never to be seen again, were captured on CCTV arguing in the hours before their apparent deaths.

Paramedic Paul Rossington, 30, jumped nearly 20 metres into the Tasman Sea after his girlfriend, Kristen Schroder, 26, apparently slipped from a fifth-level balcony on the Carnival Spirit on May 8, 2013, a coronial inquest in Sydney heard today.

But before the incident, the pair were captured on the ship’s CCTV, apparently bickering as Mr Rossington played a pokie machine.

After the short dispute, the pair shared a kiss before Ms Schroder walked away.

Her fiancé continued to play the gaming machine before leaving in a separate direction.

Police turned to lip-reading experts to decipher the footage but their attempts were ultimately unsuccessful.

Two hours later, the couple were seen arguing over dinner on the final night of the cruise, with Mr Rossington accusing his girlfriend of flirting with another man before leaving the table and heading back to their cabin.

Around 9pm, further infrared CCTV footage showed a figure in dark clothing, presumably Ms Schroder, climbing over the balcony of their cabin before apparently slipping, clinging on for four seconds, then falling, the court heard.

She tumbled 6.7 metres, struck the railing of a lower deck, and then somersaulted a further 12.6 metres into the Tasman sea.

Moments later a second figure - presumably Mr Rossington - jumps over the railing into the water.

His much brighter signature on the infrared CCTV indicates he was warm and naked when he jumped, Mr O'Keefe said, adding he had most likely been in bed then ran onto the balcony when he saw his girlfriend fall.

Mr Rossington’s act of conspicuous courage should not go unrecognised, Detective Sergeant Michael O'Keefe told the inquest.

Paul Rossington and Kristen Schroder disappeared from the deck of a cruise ship off the NSW coast on Wednesday night. (Facebook) (Facebook)

He called for Mr Rossington to be awarded the Cross of Valour.

"He must have known that jumping out would most likely end with him losing his life," Mr O'Keefe said.

A massive search began for the couple more than 16 hours later when the ship docked in Sydney and it became evident they were no longer on board.

Their bodies have never been recovered and the court heard there is little chance either survived for long.

The inquest heard the cruising holiday was "make-or-break" for their relationship of 10 months, which was described as volatile but not violent.

The inquiry was told the Coroner should find the pair’s deaths as accidental.

The Coroner is expected to recommend changes to the way the cruise ship industry deals with the issue of passengers falling overboard.