In the video, which was played to a NSW Supreme Court jury on Wednesday, McLachlan, 56, is seen placing his hand behind Samson's rear while filming season three of The Doctor Blake Mysteries in 2014.
The actor told the court he had not actually touched Samson, 32, instead claiming his behaviour was just "gags for the crew".
"I was joking with the focus pullers and the camera department to make it look like I was touching Anna's bottom. It's a joke I often did ... but I did not touch her bottom," he said.
With the Dr Blake footage showing McLachlan looking back at Samson after the alleged touching, the actor rejected claims by defence barrister Michael Hodge QC that he had fabricated the story to cover up what actually happened.
McLachlan is suing the ABC, Fairfax and actress Christie Whelan Browne for defamation over publications in January 2018 relating to claims of misconduct during the 2014 production of The Rocky Horror Show and other productions.
Mr Hodge represents the media organisations and Whelan Browne who are defending the NSW Supreme Court case on the basis of truth.
The court was played clips from a Spotlight interview by Channel Seven in May 2021 in which McLachlan discusses text messages he had found, including two that allegedly showed Whelan Browne was a bully.
During preparation for the defamation trial, McLachlan told the defendants that he did not have any relevant text messages to hand over because he had deleted them and had accidentally destroyed his smartphone in 2017.
Earlier in Wednesday's hearing, McLachlan said he was profoundly devastated by the January 2018 publications on the ABC's 7.30 and in the Sydney Morning Herald.
"I felt completely overwhelmed. I felt helpless," he told the jury.
The Gold Logie award winner said he developed extreme social anxiety as a result of the publications and was admitted into a mental health facility by the end of 2018.
"It's really a case of me barely recognising myself. And you know, without wanting to sound dramatic, every day is a struggle."
After the publications, McLachlan lost the lead role of Dr Frank N Furter in The Rocky Horror Show. Future telemovies for The Doctor Blake Mysteries, where the actor played the titular role, were also put on hold.
Under questioning by his barrister Keiran Smark SC, McLachlan denied kissing Whelan Browne in The Rocky Horror Show, pulling aside her underpants and tracing her vagina during a vertical bed scene in which the two actors' bodies were under the covers and hidden from the audience.
Allegations of improper conduct towards understudies and sound technicians were also rejected.
The reports' claims include that McLachlan called actresses into his dressing room while naked, stuck his tongue down an actress's throat during a musical number and threatened to end her career if she complained about him, and groped a crew member's breasts.
McLachlan has accused Whelan Browne and two other actresses Erika Heynatz and Angela Scundi of approaching the media for money or notoriety.
The defence case revolves around the testimony of 11 women who worked with McLachlan on the musical and on other television and theatre productions.
Witnesses set to appear for the plaintiff include the actor's partner, conductor Vanessa Scammell, several actors and around 10 reputational witnesses.
The hearing in front of Acting Justice Carolyn Simpson continues.
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