calesthio/OpenMontage · error · SystemExit

Unknown demo '{args.demo}'. Available demos: {available}

Error message

Unknown demo '{args.demo}'. Available demos: {available}

What it means

Raised by render_demo.py's main() as SystemExit when the positional demo argument names a demo that discover_demos() didn't find in PROPS_DIR. The message lists the exact available demo names, since discovery is filename-based — the argument must match a props file stem exactly (case-sensitive), with no extension.

Source

Thrown at render_demo.py:132

    )
    parser.add_argument("demo", nargs="?", help="Render one named demo instead of all demos.")
    parser.add_argument("--list", action="store_true", help="List available demo fixtures and exit.")
    args = parser.parse_args(argv)

    demos = discover_demos()
    if not demos:
        raise SystemExit(f"Error: No demo prop files were found in {PROPS_DIR}.")

    if args.list:
        print("Available zero-key demos:")
        for name in demos:
            description = DEMO_DESCRIPTIONS.get(name, "Checked-in Remotion demo")
            print(f"  {name:20} {description}")
        return 0

    if args.demo and args.demo not in demos:
        available = ", ".join(demos)
        raise SystemExit(f"Unknown demo '{args.demo}'. Available demos: {available}")

    npx_cmd = ensure_demo_environment()
    selected = {args.demo: demos[args.demo]} if args.demo else demos

    for name, props_path in selected.items():
        render_demo(name, props_path, npx_cmd)

    return 0


if __name__ == "__main__":
    sys.exit(main())

View on GitHub (pinned to 95e1c3d0ab)

Solutions

1. Copy an exact name from the error's Available demos list.
2. Run `python render_demo.py --list` to see all demos with descriptions before choosing.
3. Pass the stem only (no extension).

Example fix

# shell — before
python render_demo.py Intro.json

# shell — after
python render_demo.py --list
python render_demo.py intro

from render_demo import discover_demos

demos = discover_demos()
if args.demo and args.demo not in demos:
    raise SystemExit(f"Unknown demo {args.demo!r}. Available: {', '.join(demos)}")

from render_demo import discover_demos

def demo_exists(name: str) -> bool:
    return name in discover_demos()

When it happens

Trigger: Running `python render_demo.py mydemo` where PROPS_DIR has no mydemo props file; typo or wrong case in the demo name; including a file extension in the argument.

Common situations: Typos and casing mismatches; referencing a demo that was renamed or removed; passing the filename (e.g. 'intro.json') instead of the stem ('intro').

Related errors

• Error: {path} must define at least one cut.
• Error: No demo prop files were found in {PROPS_DIR}.
• ${res.status} ${url}
• fetch failed ${r.status}: ${url}
• path escapes project

AI-assisted analysis of calesthio/OpenMontage@95e1c3d0ab (2026-08-15). Data as JSON: /api/errors/6fb96ee741148090. Report an issue: GitHub.