ffmpeg in Universal Modder: Automatic Showcase Video Cutting

After your AI agent builds and verifies a mod, the last step is producing a shareable showcase video. Universal Modder does this with ffmpeg and a generated edit decision list (EDL) — no manual timeline editing, no video editor open.

Why ffmpeg Is a Hard Dependency

Universal Modder lists ffmpeg as a required install (alongside Python 3.10+ and uv). It's used for:

• Capturing game-only audio during in-game testing.
• Concatenating GPU-safe screenshots and short clips into a sequence.
• Adding titles, captions and beat-cut transitions.
• Exporting a compressed, shareable showcase MP4.

Without ffmpeg installed, the mod itself still builds and tests fine — but you'll miss the automatically cut video.

How the EDL Pipeline Works

1. During in-game testing, the agent captures short clips at key moments (weapon firing, explosion, new unit moving, etc.).
2. It writes an EDL (a plain-text edit decision list) describing each clip's in/out point, duration, and any title overlay.
3. It optionally generates a backing music track via fal.ai (or uses a local ComfyUI music model).
4. It invokes ffmpeg with a filter complex that assembles clips, adds beat-aligned cuts, overlays titles, and muxes the music track.

Example ffmpeg Invocation (Simplified)

ffmpeg -y \
  -i clip_01.mp4 -i clip_02.mp4 -i clip_03.mp4 \
  -i music.wav \
  -filter_complex "
    [0:v][1:v][2:v]concat=n=3:v=1:a=0[vcat];
    [vcat]drawtext=text='Fal Arsenal — Terraria':
      x=(w-tw)/2:y=h-80:fontsize=36:fontcolor=white:box=1:boxcolor=black@0.6[vout]
  " \
  -map "[vout]" -map "3:a" \
  -c:v libx264 -crf 23 -preset medium \
  -c:a aac -b:a 128k \
  showcase.mp4

In practice the agent writes this ffmpeg command automatically based on the EDL — you don't have to.

What You Get Out

• A 15–60 second showcase MP4, sized for YouTube / X / Douyin.
• Titles naming the mod and the game.
• Background music generated by fal (or local ComfyUI).
• Beat-cut transitions so it doesn't look like a raw screen recording.

Installing ffmpeg

Windows

Download the full build from ffmpeg.org, extract it, and add bin/ to your PATH. Verify:

ffmpeg -version

macOS

brew install ffmpeg

Linux

sudo apt install ffmpeg

Related