Ayden Devereux, 26, was at a house party at St Clair in Sydney's west on May 22, 2015, when a young girl arrived with a man she had met a few days before.

A court heard the teenager was nervous and felt awkward before going to the party, because she didn't know anyone there.

The girl, who cannot be named, was plied with alcohol and cannabis then taken to a small bedroom and stripped naked once she was intoxicated.

Five men stood around her while she was assaulted for at least 17 minutes.

In a judgment on Wednesday, District Court judge Christopher Hoy said the girl was raped by the men "sometimes simultaneously, sometimes consecutively", while others stood in a line adjacent to the bed.

Some of the men made crude comments, including that they would have sex with her "jail style".

One of the men said "Date rape, brother", and there was laughter as he joked about DNA.

From behind a GoPro camera one metre away, Devereux encouraged some of the men to get involved, urging one: "Let's go, get up."

"Let's go old school," he added, referring to raping the woman vaginally. "Bro, she'll do us one by one."

At stages in the video, the victim can be heard saying she is tired and wants to go to sleep. As one of the men rapes her, she says she is scared. At other times, she is almost motionless.

In August, three of the men - Tristan Carlyle-Watson, 26, Kurt Stevenson, 26, and Andrew Waters, 25 - were found guilty of aggravated sexual assault in company. They are due to be sentenced this month.

Another man, ML, who was a minor at the time of the rape, was sentenced in June to five-and-a-half years in jail with a non-parole period of three years.

Frank Kordis, who owned the GoPro and hosted the party, pleaded guilty to concealing a serious offence and was given a $3000 fine and a two-year good behaviour bond.

Mr Hoy said the girl's verbal skills were equivalent to that of an eight-and-a-half-year-old, while her non-verbal skills were that of a seven-year-old, which put her in the bottom 0.4 per cent of her peers in terms of intelligence.

There was no evidence Devereux knew of her mental impairment.

The next morning, the girl awoke naked and alone and was unable to find her clothes, underwear or mobile phone. She did not remember what had happened and made her own way home.

The "disgraceful" and "predatory" incident only came to light when some of the men involved were arrested over graffiti and the GoPro camera was seized.

Mr Hoy said Devereux knew "full well" he was participating in "vile and revolting behaviour", and his commentary on the video suggested "increasing and ongoing enthusiasm".

He said the girl was subjected to "unrelenting sexual abuse" as she became a "receptacle" for the men.

"Some of his apparent acquaintances were skulking around in that room oblivious to any sense of decency," Mr Hoy said.

"[The victim] was subjected to what could only be described as a gang-rape.

"At no time did he assist the victim. At all times he operated the GoPro."

Devereux pleaded guilty to two counts of aggravated sexual assault in company in June, days before his trial was due to start.

The court heard he decided to plead guilty after being shown the video he had filmed of the assault.

Devereux was sentenced to a maximum of seven years and six months in jail with a non-parole period of five years. His fiancee, supported by friends, cried in the public gallery.

He will be eligible for parole in October 2020.