Runway adds Mirelo SFX 2.0: automatic foley, ambience and sound effects synced to your cut

Runway now offers Mirelo SFX 2.0, which builds new sound for a finished video and keeps the dialogue. Its test results come from Mirelo's own listening panel, and Runway has not listed a price.

Runway added Mirelo SFX 2.0 on Oct 16, two days after Mirelo released it. Give it a finished video and it keeps the spoken lines, strips out music you did not ask for, and builds new sound effects and background sound timed to what is on screen.

That matters because of how sound on AI video works today. When a video model makes its own audio, the sound is baked into the clip, so changing it means generating the whole shot again and risking a take you already liked. Sound libraries cannot see the picture either, so every effect gets found, trimmed and lined up by hand. Mirelo says its model starts from the footage, keeps shots of one location sounding like the same room across cuts, and handles edits up to 10 minutes in one pass in its own app.

The numbers come from Mirelo's own blind listening test, with 25 raters judging 30 videos. Listeners preferred it to Sony's Woosh model 81% of the time, and rated it as good as or better than Seedance 2.5's built-in sound in 72% of cases. Nobody outside the company has compared it with a human sound editor yet, and Runway has not published what it costs on its platform; Mirelo's own app charges 10 credits a second until Dec 12.

In practice, you can lock the cut first and do the sound last, the way post houses always have, instead of making shots again to fix a messy track. Test it on a scene with dialogue before you trust it with a client edit.

Source: Runway on X, Mirelo blog and price list, Oct 14-16, 2026.