A federal judge in San Francisco ordered that a video of last year's trial on Proposition 8 be unsealed and made available to the public.
U.S. District Judge James Ware wrote, "Transparency is pivotal to public perception of the judiciary's legitimacy and independence."
But Ware stayed his order allowing the video's release until Sept. 30 to give the sponsors of Proposition 8, who oppose the unsealing, a chance to appeal his ruling.
A spokeswoman for the measure's sponsors and their committee, Protect Marriage, was not immediately available for comment.
Proposition 8, an initiative enacted by California voters in 2008, bans same-sex marriage in the state.
In last year's trial, now-retired U.S. District Judge Vaughn Walker found that the measure violates the federal constitutional rights of gay and lesbian couples.
The Proposition 8 sponsors are now seeking to appeal that ruling to the 9th U.S. Circuit Court of Appeals. Walker's ruling has been put on hold during the appeal.
In the meantime, trial-level issues in the case, such as the bid to unseal the videotape, have been reassigned to Ware.
The motion to unseal the video was filed by two same-sex couples who challenged Proposition 8 and the city of San Francisco. They were joined by 13 media organizations.
Ware said in today's order that the video is now part of the official record of the trial and that there is a common-law right of public access to trials.
"The court concludes that no compelling reasons exist for continued sealing of the digital recording of the trial," Ware wrote.
Walker initially planned to allow the video to be streamed live to several federal courthouses in other cities and possibly broadcast later on a government channel on YouTube.
But the U.S. Supreme Court blocked that plan by a 5-4 vote at the start of the trial in January 2010.
The Proposition 8 supporters argued that the high court's previous injunction still applies to the video.
But Ware ruled that the Supreme Court ruling was confined to "a narrow legal issue" concerning court rules.
He wrote, "The court finds that the Supreme Court's opinion does not provide compelling reasons to overcome the strong presumption in favor of public access to the digital recording, now that the trial is over and the digital recording has entered the public record."
Ware's decision can be appealed to the 9th Circuit and then to the U.S Supreme Court.
The two same-sex couples' lawsuit was sponsored by the Los Angeles-based American Foundation for Equal Rights.
Foundation board president Chad Griffin issued a statement saying, "This is a significant victory for the American people, who will soon be able to see the evidence put forward by both sides in this historic federal trial."