"Kem Sokha will be the victim of a staged trial on completely bogus treason charges", Robertson said.
Mr Sokha's lawyers have asked for the full, hour-long version to be shown.
The trial is expected to take up to three months, meeting twice a week, according to a report by the USA -government-funded Voice of America quoting Phnom Penh Municipal Court President Taing Sunlay.
"An acquittal would undermine the government's accusation of treason", she said.
Kem Sokha's daughter, Kem Monovithya, yesterday decried the proceedings.
Meng Sopheary said Kem Sokha continues to maintain his innocence and that her own study of his case shows "there is no evidence to convict my client".More news: PGA Tour implements stricter policy, harsher penalties to prevent slow play
"But clearly Prime Minister Hun Sen decided instead to extract the proverbial pound of flesh from Kem Sokha for daring to challenge him", he stated in a press release of the opposition chief, who faces as much as 30 years in jail if discovered responsible.
"During the next hearing, I request the court to allow at least one journalist from each institution to attend the trial", he said.
Astrid Noren-Nilsson, an associate senior lecturer at the Centre for East and Southeast Asian Studies at Sweden's Lund University, said there was little chance Sokha would be acquitted. Ky Tech did not specify whether the court plans to summon representatives of those countries to appear at the trial.
Sokha was arrested for treason at his house in Phnom Penh in the middle of the night on September 4, 2017.
He was freed from house arrest in November but banned from engaging in political activities.
The transfer to dissolve the CNRP was half of a wider crackdown by Hun Sen on the political opposition, NGOs, and the unbiased media that paved the way in which for his ruling Cambodian People's Party (CPP) to win all 125 seats in parliament within the nation's July 2018 common election.
"I categorically deny the charge of "conspiracy with foreign powers" which was brought against me", he said. Rights groups, journalists and civil society organizations criticized the restrictions. "I want justice to come swiftly".More news: ‘Friends’ reunion in jeopardy on HBO Max
More than two years since his arrest on treason charges, the trial of Cambodian opposition leader Kem Sokha began Wednesday in a case that has repercussions for the country's trade privileges with Europe.
Critics from across the world called the trial a "circus".
"Kem Sokha's charges must be voided and the rights of CNRP members must be fully respected to enable them to freely participate without discrimination in Cambodia's political life once again", he stated. "That's why we have to support him".
"Over the past three years, the Cambodian authorities have weaponised the criminal justice system as a means of eliminating the CNRP".
Since 2017, the CNRP has faced politically-motivated accusations that it has colluded with the United States government to foment a so-called "colour revolution", characterised as a coup by the Cambodian authorities.
Villarin said that Cambodia's courts routinely demonstrate that they act according to Hun Sen's interests, rather than based on the facts and evidence presented to them. Along with the American officials, a coalition of 82 Cambodian civil society groups has also urged the court to open the trial for public, independent media and civil society groups.
"The European Union has repeatedly raised Kem Sokha's case in the context of an ongoing review of Cambodia's trade preferences", said Phil Robertson, Human Rights Watch's deputy Asia director.More news: An 'unprecedented' 31 million people downloaded the Disney+ app in Q4 2019