The video, obtained by extremist monitoring organization SITE, shows Norwegian national Kjartan Sekkingstad, Canadian national Robert Hall and Filipina Marites Flor sitting on the ground, surrounded by six armed militants, one of whose faces is masked.
Sekkingstad was the resort's manager, while the other three hostages were guests who had docked their yacht at the resort's marina.
The video then pans to Hall, who asks the Filipino government to stop its military actions against the group, implying that the offensive is putting their lives in danger. Operations against Abu Sayyaf were stepped up in the wake of Ridsdel's murder.
Hall says that he's been told to demand that the Canadian government pay their ransom, and cites the inaction of the Trudeau administration as a cause of Ridsdel's death.
Further decapitations threatened
The only masked militant then addresses the camera, who says that the lesson of Ridsdel's death was clear and warns against procrastinating in the negotiations, threatening to behead the three remaining hostages if their demands are not met.
Four Indonesians were still being held, Indonesian President Joko Widodo said, and his government would continue to work to secure their release.
Who are Abu Sayyaf?
The violent extremist group seeks to establish an independent Islamic state on Mindanao, the southernmost major island of the predominantly Catholic Philippines.
The Philippines military has made inroads in recent years in thwarting the group's terrorist bombing campaigns, prompting a shift in focus by the group to kidnappings for ransom.
Greg Poling, director of the Asia Maritime Transparency Initiative at the Washington-based Center for Strategic International Studies, has said that "after about 15 years of a pretty harsh crackdown by the U.S. and the Philippines, what they've basically become is a criminal group made up of a few hundred who engage in extortion and kidnapping."
CNN's Chieu Luu and Rebecca Wright contributed to this report.
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