A full-time national serviceman - already given a conditional warning for attempting to record a video up the skirt of a woman - was trying on clothes in a Cotton On fitting room when he decided to film a female student in the next changing room.

Yesterday, Darren Tan Yong Xing, 26, was jailed for 12 weeks for insulting the modesty of the 21-year-old student at the clothing store's VivoCity outlet, and for trying to record a video up the skirt of a 32-year-old bank officer at Yio Chu Kang MRT station.

He was also fined $2,000 for having four obscene films on April 30 last year.

Five other charges were considered during sentencing.

The court heard that Tan was trying on some clothes on April 30 last year when he noticed a woman entering the room next to his and decided to film her.

After she had left, he remained in the room to try his luck again.

The 21-year-old student was next to use the fitting room to try on lingerie.

After a while, she noticed a mobile phone being held under the partition, with its screen facing up and in recording mode.

When he realised he had been found out, Tan quickly left the changing room but was caught by the victim. She called out to the staff for help.

When police checked Tan's phone, they found a video clip of the victim topless, along with a number of other obscene videos.

Tan committed the offences while he was still under a 12-month conditional warning for attempting to take the video of the bank officer at about 7.40am on July 14, 2014.

While the victim was on the escalator at the train station, she felt someone standing close behind her and a tugging sensation on her dress. She turned around and saw Tan holding his mobile phone beneath her dress.

He rushed onto the MRT platform and ran down the stairs before she could stop him.

The police managed to establish his identity and arrested him later.