Showcase video

A mod isn't finished until you can show it in 30 seconds. The toolchain is um win record (capture), um video contact (look), um video compile (edit), all ffmpeg + Pillow.

1. Make the take repeatable

• Script the action. Use a mod-side timeline or command sequence (spawn enemies, fire the weapon, cue the boss), a scenario with triggers and camera moves, or a WinDrive command list. The first clean take should be reproducible exactly, so you can reshoot after a fix.
• Restore the world before each take. Explosions crater worlds; units die. Keep a pristine copy with um backup and restore it every take.
• Clean frame. Hide debug text, fix the camera zoom (the Terraria showcase used 1.5x so 1080p frames read like a 720p cut), run at full speed when unfocused, and hide the cursor (capture uses capture_cursor=0).

2. Record the window + the game's own audio

um win record --exe Game.exe --out C:\caps\take1 --seconds 40      # -> take1.mkv, take1.audio.raw, take1.json
um video first-frame C:/caps/take1.mkv                              # where gameplay starts (skips loading screens)
um video mux C:/caps/take1.mkv C:/caps/take1.audio.raw C:/caps/take1.json take1.mp4 [--offset 0.25]

• Video: ffmpeg gfxcapture of that window only (GPU frames, no desktop). It encodes with NVENC, AMF or QSV when available. NVENC H.264 maxes out at 4096 px wide, so the recorder scales above that; for 32:9 screens, crop to the centre 16:9 with --crop.
• Audio: WASAPI process loopback of the game's PID (um/ps1/ProcLoopback.ps1). Only the game is recorded; no Spotify, no notifications. It's timestamped so the file position is wall time. Muxing uses the recorded offset. Fine-tune with a visual/audio sync event (a flash vs its boom) and pass --offset.
• Inside a mod (optional): start and stop recording from the mod for frame-exact takes. Never block the game's main thread while stopping ffmpeg: send q, then wait off-thread. Write .mkv so a killed recorder still leaves a playable file (see examples/terraria-tmodloader/reference/InModRecorder.cs).

3. Look before you cut

um video probe clip.mp4
um video contact clip.mp4 sheet.png --every 1.5 --cols 6     # a timestamped grid; read it, pick in/out points
um video contact clip.mp4 zoom.png --start 20 --end 30 --every 0.5

Pick the peak moments: the explosion, the boss reveal, the unit in formation. Write in/out times into the EDL.

4. Edit with an EDL

um video compile edl.json out.mp4 (--preview renders half size and fast). The full format is in um video --help.

{
  "size": [1920, 1080], "fps": 30,
  "theme": {"accent": "#B6FF3B"},
  "transition": {"type": "fade", "duration": 0.3},
  "clip_volume": 0.8,
  "music": {"path": "music.mp3", "volume": 0.5},
  "watermark": {"path": "logo.png", "height": 54, "corner": "br"},
  "segments": [
    {"clip": "take1.mp4", "in": 9.0, "dur": 3.0, "hook": "Terraria, but with a tactical nuke."},
    {"clip": "take1.mp4", "in": 24.2, "dur": 4.5, "title": "Tactical Nuke", "transition": {"type": "pixelize"}},
    {"clip": "take2.mp4", "in": 3.0, "dur": 5.0, "title": "Drone Mothership boss"},
    {"card": {"title": "Fal Arsenal", "sub": "a Terraria mod"}, "dur": 2.5}
  ]
}

• Transitions: any ffmpeg xfade type (fade, pixelize, slideleft, smoothleft, circleopen, zoomin, radial...) or cut.
• Fills: for non-16:9 clips, fill: blur (blurred backdrop), crop or pad.
• Per clip: speed and volume, zoom to punch in past UI, crop [x, y, w, h] to reframe.
• Music: um fal music "..." --seconds 60 makes a bed. Set bpm and use beats instead of dur to cut on the beat; um video beats music.mp3 estimates tempo and first beat.

Style that works (from real feedback)

• Titles: one line naming what's on screen ("Wonder: the Transamerica Pyramid", "Robotaxis and Delivery Drones"). No small explanatory captions about how it was made; that goes in the post text.
• Pace: get into gameplay within 2-3 s; menus and setup stay under 3 s. Clips run 3-5 s each. End on the mod name or URL and fade out.
• Sound: keep the game's audio. It sells impacts. Music under a compilation, clip audio around 0.5-0.8.
• Compilations of other people's clips: credit every creator on screen (credit: "@handle") and in the post, and ask permission when it's promotional. Don't imply their clips were made with your tool. Download only public posts, and only what you'll use.
• Last step: look at a contact sheet of the finished video before sharing it.