A man who beat a dog so brutally he broke its neck can be seen in surveillance footage of the attack smiling, prosecutors told a court Friday.

Prosecutors described the man's smile as chilling after the sickening footage was played to the ACT Magistrates Court. The man, 27, pleaded guilty to aggravated cruelty to an animal and has been in custody since his arrest in August.

In the footage, the man, who has not been named because the offence is one of family violence, can be seen throwing the dog across the yard, beating it with his fists and open hands, returning to the at times motionless dog and kicking it, and holding it down as he delivered even more blows.

The attack lasted just over 10 minutes, and in between beatings the dog is seen cowering in the corner of the fenced yard or lying motionless.

The dog had to be put down.

The length of the attack and its pauses led Acting Chief Magistrate Glenn Theakston to conclude it was not a loss of self control but a calculated and deliberate attack by a person who appeared unsatisfied after each bout.

The attack had no apparent justification or reason, Mr Theakston said.

The magistrate convicted the man and sentenced him to four months' jail, to serve three months.

He also banned the man from buying or owning animals for five years.

A victim impact statement from the dog's owner, who is the mother of the man's partner, described a much-loved and cared for pet and "soulmate".

She said when they took the "brutally tortured and bashed" dog to the vet after the attack she was in pain and paralysed.

An X-ray revealed a broken neck, and the vet's difficult prognosis was that even with an $8,000 to $15,000 surgery the dog's survival was not certain.

"I was hysterical," she said about being put in the position to play God.

"I had to put Mishka to sleep.

"I knew it was the kindest thing I could do for her."

A lawyer for the man said at the time of the attack he had been frustrated by his volatile relationship with his partner, incompetent colleagues at his work who were putting others at risk, and damage caused by the dog to his belongings.

The lawyer added that was not to excuse his behaviour but to show what was on his mind.

The lawyer said the man had been unable to watch to footage as it was played to court and said this, along with his admissions and plea of guilty, was a sign of remorse.

But the prosecutor called for time in jail.

She said that at one point the man can be seen smiling as he walks past the camera, which was "particularly chilling".

It was an inexplicable and unacceptable attack on a vulnerable creature who could not escape, she said.

She noted the man had turned from the footage as it was being played in court but disagreed with the defence that it was a sign of remorse.

She said the footage was horrible and he didn't want to be reminded of what he had done.