Tandem: an MIT video editor with a CLI and MCP, where agent edits stay purple until you've watched them

This is the second 'I had Claude build my editor' video today, after Ben Vallack's, and this one ships code. Mike Cann makes the Convex YouTube channel's videos. He edited them in Filmora until he hit a wall: no API or MCP, and hacking its project files meant reloading the app after every agent change. So he gave Opus 5.5 a spec and went to bed. He says it made over 200 commits overnight and needed a day or two of back and forth after that. He has edited seven videos in Tandem since, including this one, live on camera.

Per the README, Tandem is a Swift app for macOS 15+ (some transcription features need macOS 26). A project is a single .tandem JSON file in the video's folder. The app pairs camera and screen takes, makes transcripts and waveforms, and does the speaker cutout in the background. Agents edit the same project through a CLI or an MCP server (claude mcp add tandem ...), and install.sh links a Tandem skill into Claude Code and Codex. Stickers, music, looks and fonts live in a shared library. It imports old Filmora projects and agent-written EDLs, and the video shows it calling ElevenLabs for music and sound effects.

The idea worth copying is the review gate. Anything the agent touches turns purple on the timeline and in a strip above it, so you only rewatch what changed, not the whole 20 minutes. Before the agent accepts new instructions, you have to mark its changes as reviewed. That stops you sending notes on footage you haven't seen. You leave notes as timeline comments ('looks like a bad take here'), and in the video the agent then hunts down similar false starts across the whole cut. He's honest that it still misses some retakes on the first pass.

It's deliberately a personal tool. He doesn't take issues or pull requests, and the README tells your agent to fork it and adapt it to your setup. If you'd rather not maintain your own editor, BaoCut and our editors roundup are the ready-made route. If you're on a Mac and like the idea, this is the most complete open starting point we've seen. Based on the creator's video and README, not tested by us. Credit Mike Cann.