The video shows a young white woman in the bath, in pyjamas, being assaulted by a girl in dark clothing.
The suspect has dark hair tied in a bun and appears to be wearing distinctive false eyelashes and black and white patterned ankle boots.
A second woman watches the attack and also takes part in it.
Det Insp Shane Ahmed, of Cardiff CID, said: "In the video, this girl is being absolutely beaten in a bath.
"She is repeatedly punched, kicked, her neck is stamped on, her head is hit against the bath," he told Cardiff-based Media Wales.
"The attack appears to continue after she falls unconscious, with bathroom detergents poured over her," he said.
"It is a horrendous, prolonged attack and it is made even more worrying by the fact that we don't know who the victim is, where the attack has taken place or even if she is alive and breathing now.
I can get any amount of kittens for free, should you need one in future. They're rescue ones (not liberated)
cat found and recoveredhow much outrage is there going to be about this!
Woman steals kitten from pet shop by putting it in handbag!
http://www.walesonline.co.uk/news/n...-into-bag-at-cardiff-pet-shop-91466-32569180/
will it get as big as cat bin woman? definately going to go national init.
It's a celebrity cat now!
A death in Cardiff city centre has sparked a police investigation.
Officers cordoned off a section of the city centre and a police tent was erected outside a pub.
It is understood one person has died.
Police were conducting an examination outside O'Neill's Bar in St Mary Street early on Monday morning following the death.
By about 9am, a tent was erected at the scene near the scaffolding in place at the front of the bar.
South Wales Police said they would be issuing a statement on the incident later on Monday.
Adonis kebab owner imprisoned for the E. coli thing last year
8 months!
http://www.bbc.co.uk/news/uk-wales-south-east-wales-21020204
i couldn't believe people going in there when it reopened