Who are they
Sia is an ozzie singer she's more famous worldwide for doing collaborations with various DJs especially DJS involved in dance music aka trance, handsup etc.
One such DJ is david Guetta who has collaborated with various famous artists and not so famous ones.
His music videos are more of the artistic variety rather than the typical pop artist type what this means is that they will show videos totally unrelated to the artist and the artist themselves might not even feature in the video which isn't unusual cos western music has always been like that ever since mtv became popular. One example would be guns N roses albums where they show all the band with their head gear but their faces replaced by skills instead. This is very tame but if you compare it to say Chinese music it's totally outrageous.
Anyway back to SIA she's famous for these 2 songs.
notice she doesn't even appear in these 2 videos
Also what is titanium in sg's context?
Yup it's a type of ah beng song where ppl chant their own gang lyrics.