Former Labour MP Eric Joyce has pleaded guilty to making an indecent photograph of a child.
The 59-year-old former shadow minister, who was MP in Falkirk between 2000 and 2015, has been ordered to sign the Sex Offenders Register.
Joyce, of Worlingworth, Suffolk, admitted making an indecent photograph of a child between 7 August 2013 and 6 November 2018 at a pre-trial hearing at Ipswich Crown Court.
Judge Emma Peters said the single 51-second video, found on a device, "depicts a number of children".
"Some are quite young, one is said to be 12 months old," she said.
"Clearly a category A movie."
A category A offence - the highest possible for indecent images of children - is defined as "images involving penetrative sexual activity or possession of images involving sexual activity with an animal or sadism".
The judge said Joyce said he accessed the video "via an email which he says was a spam email".
"At the time he was drinking heavily and he has now undergone work with the Lucy Faithfull Foundation and a psychotherapist," she added.
Joyce, who was a Labour MP for 12 years and an independent for his final three, was granted bail and the judge instructed that a report be prepared before he is sentenced on 7 August.
The judge warned Joyce the offence crosses the custody threshold.
"It's going to be a question of whether it's immediate or suspended," she said.
"You will be required to sign paperwork today acknowledging that you are immediately on the sex offenders register," she said.
She said the court "takes such incidents very seriously" as they "fuel the abuse of children".
Joyce stepped down as an MP before the 2015 general election and had spent 21 years in the Army, rising to the rank of major, before going into politics.
A statement on his website last month said he would "make a full statement" when "all legal processes are at a close".