Tape Demo

tape-demo

Produce a reproducible scripted terminal demo: write a VHS .tape file that describes the session (settings, typed commands, pauses), then render it to GIF/MP4 with vhs. The tape is source code — commit it next to the artifact so the demo regenerates the same way after every CLI change (reproducible given the same tool versions, fonts, and environment). No live recording, no typos, no personal shell state on screen.

When NOT to use

• Capturing a real session's authentic output/timing → cast-record.
• Converting or restyling an existing .cast recording → cast-render.
• Removing secrets from a recording → cast-redact.
• Browser/GUI walkthroughs — VHS drives a terminal only.

Decision rule: no recording exists yet and the goal is a polished README/docs demo → this skill.

Workflow

1. Plan the story. Pick 2–5 commands that showcase the tool; run them once yourself to know the real output and timing. Add Require <program> lines for every binary the demo needs.
2. Write the tape. Start from ${CLAUDE_SKILL_DIR}/assets/demo-template.tape (neutral theme, README-friendly geometry) or vhs new demo.tape. Rules:
   • Output demo.gif (+ Output demo.mp4 for both formats in one run).
   • All Set lines at the top: any setting except TypingSpeed placed after a non-setting command is silently ignored.
   • Type/act: Type "cmd", Enter, Sleep 500ms, Up/Down, Ctrl+C, Type@250ms "slow" for per-command speed.
   • Variable-duration steps (installs, builds, network): use Wait /pattern/ on expected output instead of guessing a Sleep. Default scope is the last line, default timeout 15s (Set WaitTimeout 30s to raise; Wait+Screen /pattern/ matches the whole screen).
   • Setup/cleanup the viewer shouldn't see goes in a Hide … Show block (e.g. build the binary, clear).
3. Secrets and safety. A tape is executable code — review every command before rendering, and run in a clean directory. Hide only stops frame capture; the command still runs and its values persist in the session, so use obviously fake values (Env API_TOKEN "demo-token-123"), never real credentials, even hidden.
4. Validate, then render.

   vhs validate demo.tape   # parse check, no execution
   vhs demo.tape            # renders every Output
   

5. Check the artifact. Confirm outputs exist; keep README GIFs under GitHub's 10 MB image budget (shrink via Set Framerate 10, smaller Width/Height, or gifsicle — see cast-render for GIF optimization). Re-render after any tape edit; that's the point.
6. Optional CI regeneration: charmbracelet/vhs-action@v2 re-renders tapes in GitHub Actions so demos never drift from the CLI.

Theming (templateable look & feel)

• Neutral default: Set Theme "GitHub Dark" (or "Dracula", "Catppuccin Mocha", … — vhs themes lists all ~348 bundled names).
• Project brand: inline JSON theme with your palette:

  Set Theme { "background": "#29283b", "foreground": "#b3b0d6", "black": "#535178", "red": "#ef6487", "green": "#5eca89", "yellow": "#fdd877", "blue": "#65aef7", "magenta": "#aa7ff0", "cyan": "#43c1be", "white": "#ffffff", "brightBlack": "#535178", "brightRed": "#ef6487", "brightGreen": "#5eca89", "brightYellow": "#fdd877", "brightBlue": "#65aef7", "brightMagenta": "#aa7ff0", "brightCyan": "#43c1be", "brightWhite": "#ffffff", "cursor": "#b3b0d6", "selection": "#3d3c58" }
  

• Window chrome: Set WindowBar Colorful, Set BorderRadius 8, Set Margin 20 + Set MarginFill "#674EFF" for a framed hero look.

Output spec

• demo.tape committed in the repo (reviewable diff), artifacts (.gif/.mp4) regenerated from it — never hand-edited.
• vhs validate passes; render succeeds; GIF within size budget.
• No real credential, hostname, or personal path appears in the tape or render.

Gotchas

• VHS renders in a headless browser (ttyd + Chromium): Set FontFamily only works for system-installed fonts; missing fonts fall back and can break spacing. brew install ttyd ffmpeg are required alongside vhs.
• GIF is capped at 256 colors — rich themes dither. Prefer MP4 for color-heavy demos, or drop Set Framerate to 5–10 and post-optimize.
• vhs record > cassette.tape bootstraps a tape from your real keystrokes — fastest way to discover the command sequence; clean it up afterwards.
• Multiple Output lines render all formats in one run; .txt/.ascii outputs give golden files for CI diffing.
• Shell matters: Set Shell "bash" avoids surprises from personal zsh/fish config; an unthemed prompt keeps the demo neutral.
• Verified against VHS v0.10.0–v0.11.0 (v0.11.0 added ScrollUp/ScrollDown).

Full verified command/setting reference: references/tape-reference.md. Starter template: assets/demo-template.tape.