At the start of the trailer, audio from her June conservatorship testimony plays over the pop star standing on stage.

"I deserve to have the same rights as anybody does," the 39-year-old voice says in the voiceover. "It's been 13 years and it's enough."

It is not clear from the trailer how many figures in the hitmaker's circle will appear in the film. Her former partner, Adnan Ghalib, and her former assistant, Felicia Culotta, appear briefly on screen.

The minute-and-a-half long trailer comes a week before the Stronger hitmaker will appear in court for her next conservatorship hearing. The documentary is set to premiere on 28 September, a day before the hearing.

It is the second documentary about the case, after The New York Times released Framing Britney Spears in February.

Erin Lee Carr, who directs the film, was asked by the Los Angeles Times what the major differences between the two documentaries will be.

"This is a two-and-a-half years-long investigative process into the conservatorship," Carr explained. "There has been an amazing amount of coverage, but that's a really long time to be focused on this. We wanted to be the definitive place to understand the beginning, middle and hopefully what we will find out as the end of this saga."

The documentary comes weeks after Spears' father, Jamie, filed a petition to end the 13-year conservatorship. The reversal was a major change for the 69-year-old, who had argued that the pop star was not ready to be released from the all-encompassing legal arrangement.

In her June testimony, the mother of two claimed the conservatorship stopped her from having more children or getting remarried. Shortly after Jamie agreed to end the conservatorship, Spears announced her engagement to her longtime partner, actor Sam Asghari.