"The offending arose out of an extensive sexual experimentation between the couple in which they engaged in risque activities," he said.
"From the perspective of Ms Thredgold, she thought that that was something her partner wanted and it's quite apparent that, from Mr Thredgold's perspective, that is also what he believed."
Marcus said the videos were never distributed and were only discovered by police after Rebecca Thredgold handed over the hard drive during an unrelated investigation.
"This is grossly unsophisticated offending," Marcus said.
He said his client, a mother of six children, was unaware of the magnitude of the crime, which Judge Simon Stretton said he could believe because the offence was "very rare".
"It is so rare I'm sure that most people wouldn't be aware of the degree to which the law does disapprove of it," the judge said.
"It's an affront to public dignity."
Oliver Cole, for Kevin Thredgold, said his client, 48, has also suffered "a significant level of embarrassment".
"It was a relationship where they were exploring their sexual boundaries," he said.
Prosecutor Georgina Venn said the crime was too serious for the pair to be handed a suspended or home detention sentence.
"The offending is undoubtedly serious and … morally repugnant in nature.
"It's obviously a highly unnatural activity for a dog to be engaged in."
Venn said it was not clear whether the dog was harmed because it had died by the time the videos were discovered.
The pair, who are now living separately, each pleaded guilty to two counts of bestiality and will be sentenced later this month.
Rebecca Thredgold had covered her face and made no comment as she left court.
