Former Labour MP Eric Joyce has pleaded guilty at Ipswich Crown Court to making an indecent photograph of a child
Joyce, 59, was MP for Falkirk between 2000 and 2012.
The former shadow minister, of Worlingworth, Suffolk, was arrested in November 2018, said police.
He has now been instructed to sign the sex offenders register.
The charge against Mr Joyce alleged that, between 7 August 2013 and 6 November 2018, he made an indecent photograph of a child.
Judge Emma Peters said that the single 51-second movie, 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.”
Former shadow minister Joyce, of Worlingworth, Suffolk, was granted bail.
Judge Peters instructed that a report be prepared before Joyce is sentenced on August 7.
Prosecutors said the file, found on a device, was a movie file classed as a Category A image.
He also held the post of shadow Northern Ireland minister in 2010.
He left the party to serve as an independent MP in 2012, stepping down in 2015
Mr Joyce joined the army in 1977, serving for 21 years and rising to the rank of major.