tvN tried AI to replace an actor on Signal 2 and failed

Second Signal, the tvN drama held back after its lead actor's career ended in controversy, will premiere on December 7, 2026 with his scenes intact. tvN tested replacing him with AI and decided it could not. Months earlier, a rival Korean network used the same technology to build three minutes of a drama that a live shoot could not have afforded.

The channel announced the schedule in an official statement on November 6, 2026, as Star News and Chosun Biz both reported. The show, also written Signal 2, is the sequel to the 2016 mystery drama Signal, which drew a peak viewership rating of 15%. Cho Jin-woong had completed filming as detective Lee Jae-han, the character he played in the first season. In December 2025, reports about a juvenile record led him to announce his retirement, and he admitted past wrongdoing and apologized.

What tvN tested

tvN said it explored two routes to keep the finished drama usable, and neither held up. In the statement, read in full at the Korean-language outlet Spotvnews, the channel said it "explored revision options using video technology and conducted tests for character replacement utilizing AI," and that "due to limitations in naturally realizing acting expressions and narrative flow, final application of the technology proved difficult."

The scenes featuring Cho Jin-woong will air as they were shot, without separate edits, Chosun Biz reported. tvN also addressed why it is releasing the show at all. "Releasing the work does not mean defending or justifying a particular cast member's past conduct," the channel said, in Chosun Biz's translation, adding that it weighed the viewers who had waited for the drama and the actors and staff who finished it.

The rollout is unusual. Signal 2 runs eight episodes, and the first three land in the opening week: on December 7, a shortened episode 1 airs back to back with episode 2, then episode 3 follows on December 8, after which one episode runs each Monday and Tuesday. tvN set the broadcast at 10 p.m. KST, later than its original slot, citing the show's genre and viewing conditions, per SBS News.

Why replacing an actor is the hard version of the job

The channel's stated reason is narrow and specific. The tests did not fail on faces or on resolution. They failed on acting expression and on the flow of the story, which are the parts of a performance that a replacement has to reproduce rather than invent.

That is the harder task by design. Replacing an actor means every shot that features him has to be rebuilt to match a performance that was already recorded, in a scene that was already cut, beside actors who were already reacting to him. The model is not asked to imagine a detective; it is asked to reproduce one man's face, timing and weight across a full part, and to keep all of it consistent from episode to episode.

tvN has published no footage of the tests and no technical detail beyond the statement, so there is no way to see how close the attempts came. The statement is the entire public record of the effort.

What Chief Kim did instead

The comparison that gives the tvN decision its shape is SBS's Chief Kim, which ran from June 26 to July 25, 2026, per Wikipedia. According to Morpheus Studio, the video-technology and production company on the show, Chief Kim produced an entire sequence of roughly three minutes depicting the protagonist's past entirely with AI, and it aired split across episodes 1 and 2, Star News reported.

The sequence covers Chief Kim's past after he was recruited as an operative from North Korea and sent there on a special mission. Star News lists what it contains: building demolitions, car chases on snow-covered roads and in tunnels, vehicle rollovers and crash scenes, underwater scenes in which a car breaks through a railing and submerges in river water before the vehicle is recovered, gunfights and action scenes featuring So Ji-sub and other characters, and close-ups of the characters' expressions. The report credits the work with holding character consistency and completing a scene of that length, two problems long cited as hard for AI video.

Morpheus Studio says the length is the point. Star News attributes the claim to the company: this was the first time in Korean drama history that a sequence this long was realized entirely through this method. The Asia Business Daily reports the same framing, sourced to the production company, and notes the scene would otherwise have needed spending on set construction, outdoor locations, explosions, special effects and post-production VFX.

The two jobs are not the same. Chief Kim had no actor's footage to preserve. It had a scene that was never shot, and it built that scene from nothing, which is where a generative model is strongest.

How Morpheus Studio built the sequence

Ryu Jaehwan, Vice President of Morpheus Studio, told The Asia Business Daily what the team was aiming at. "What's important is not simply replacing several seconds of VFX with AI, but rather using AI to produce the entire sequence necessary for narrative completeness," he said, adding that the Chief Kim team had a clear plan for how to use AI video from early in planning.

The workflow is documented in outline. The Asia Business Daily reports that video professionals pre-design each scene, combine multiple generative models, and repeatedly review whether characters and spaces flow naturally. Morpheus Studio's production platform, Aichron, released in February 2026, lets a team combine several AI models for prompt input, image, video and sound generation, plus editing, inside one workflow, the outlet reports. Wikipedia lists the platform as AICRON and dates it to February 2026.

None of this is a button. The published accounts describe a crew shaping each shot and checking the output, which is why the sequence reads as a production rather than a demo.

What it means for AI video creators

The lesson in the pairing is about the shape of the job, not about whether AI video works. Chief Kim asked a model to create a scene that did not exist, and the team got three minutes of demolition, chases and gunfights out of it. tvN asked a model to stand in for a specific actor across a finished drama, and the attempt fell short on the performance itself.

If that reading holds, the practical rule for creators is to point these tools at the parts of a story that have not been filmed. A generated establishing sequence, an action beat that was never affordable, a backstory shot without a cast, all sit in the zone Chief Kim proved out. Swapping a named performer out of footage that already exists is the case that, on tvN's own account, did not clear the bar.

Two caveats are worth keeping. The "first in Korean drama history" claim comes from Morpheus Studio and the outlets reporting its account, not from an independent body, and tvN has not said how much of the drama its tests covered or how close they came. The record here is two company statements and the reporting around them.

Signal 2 premieres December 7 on tvN at 10 p.m. KST, with a shortened episode 1 running back to back with episode 2 that night.