Video: 'Lose Yourself' co-writer plays tune in court

An Oscar and Grammy-winning co-writer of Eminem's hit song 'Lose Yourself' has appeared in person in a Wellington Court.

Producer Jeff Bass has been called as a witness in the copyright case brought against the National Party over the alleged use of the rapper's song.

The hearing between Eight Mile Style and the National Party began in the Wellington High Court on Monday, and is set down for six days.

The court was told the National Party breached copyright by using a piece of production music in a 2014 election advertisement which resembled Eminem's 'Lose Yourself'.

Bass has won multiple awards for his work with Eminem - including an Oscar in 2003.

He gave evidence to eight lawyers and a judge via an acoustic guitar, and said the National Party's use of the track 'Eminem Esque' in a 2014 election advertisement was a blatant ripoff of 'Lose Yourself'.

The current hearing is set down to decide whether copyright was breached or not. Any decision on damages will be dealt with at a later date.

National has rejected the allegation.

Bass said he and the other composers of the track have turned down huge offers to license the song for political purposes.

In 2014, National claimed the track had been used on several television shows, and Eminem's publishers did not complain about any other use of it.

Steven Joyce also called the use of the track "pretty legal" - a statement which was famously mocked by comedian John Oliver.

Eight Mile Style LLC is a copyright administrator, which protects and enforces composers' rights as well as collects income on their behalf.