promoshot

See it work: demo.md — twenty-four prompts, each given to a fresh agent with only the skill and the MCP, its result beside the hand-built reference. The suite is in demos/.

The rendering engine behind PromoShot (App Store), and an open implementation of its project format. A .promo project is a folder — metadata.json plus its media — and this workspace is everything needed to validate, inspect, and render one to stills, image sequences, or mp4 with mixed audio: no app attached, byte-for-byte the same compositor the apps ship.

The design bet is that the format is the interface. An assistant, a script, or a person writes metadata.json; the engine renders it the same everywhere — the Mac and iOS apps (Metal + VideoToolbox), this repo's CLI, or a headless Linux box with no GPU at all (wgpu on lavapipe, ffmpeg as a subprocess). The format has three faces behind one truth: an authoring subset with four validated recipes (promo schema), the full document (--full), and a types-only JSON Schema generated from the parser's own structs (--types) — and the parser the validator runs is the parser the renderers use, so "validates" means "renders".

Crates

Build and verify

./check-all.sh          # fmt, clippy -D warnings, all tests, release build

Rendering video needs ffmpeg (and ffprobe) on PATH — frames are composited on the GPU and piped to it raw; ffmpeg only decodes and encodes. On a headless Linux machine, mesa-vulkan-drivers (lavapipe) is enough of a GPU.

The CLI

cargo build --release -p promo-cli     # -> target/release/promo

promo schema                            # authoring subset + recipes; --full, --types
promo validate <project>                # exit 0 == this will render
promo inspect  <project>                # canvas, layers, missing media, undefined colours
promo still    <project> --out f.png --time 2.5
promo frames   <project> --out frames/ --fps 30 --from 0 --to 4
promo video    <project> --out out.mp4 --fps 30

Add --json to any project command for machine output — one object on stdout, errors included, exit codes unchanged.

promo video mixes the soundtrack the apps would: trims and media cuts, held frames, speed with pitch preserved, keyframed volume, a focused narration ducking everything under it, and only the audio tracks the project keeps.

Headless renders are CLEAN — no watermark, and no license, serial or key will ever be asked for. (The Mac and iOS apps watermark free-tier renders; that is their App Store Pro line, and it stays on their side of the fence.)

The MCP server

promoshot-mcp speaks Model Context Protocol over stdio, so any MCP client can author, inspect and render projects. It owns no rendering code — every render shells to promo (found next to the executable, or on PATH, or via --promo), so the CLI stays the single contract.

Connect an agent

Two pieces: the MCP server (tools) and the skill (workflow). Neither is vendor-specific. Agents do not find this repo by themselves.

1. Build — or don't

cargo build --release -p promo-cli -p promoshot-mcp
# binaries: target/release/promo  target/release/promoshot-mcp

No Rust toolchain? Grab the prebuilt pair from Releases (linux-x64, macos-arm64), or pull the image: docker pull ghcr.io/garalex/promoshot-mcp — both carry promo and promoshot-mcp together.

Put both on PATH, or pass --promo to the server. Rendering video also wants ffmpeg/ffprobe on PATH.

2. MCP (required for tools)

Claude Code / Cursor / any mcp.json:

{
  "mcpServers": {
    "promoshot": {
      "command": "/ABS/PATH/target/release/promoshot-mcp",
      "args": ["--workspace", "/ABS/PATH/Promo", "--root", "/ABS/PATH/Promo"]
    }
  }
}

--workspace is where new projects go; --root fences which projects the server will touch — pointing both at one folder is the tidy setup. Both optional. --log <file> appends one line per tool call — when, which tool, how many milliseconds, how it went — for a session's own accounting; the demo pages are built from it.

Client one-liners:

# Claude Code
claude mcp add promoshot /ABS/PATH/target/release/promoshot-mcp

# Grok Build
grok mcp add promoshot -- /ABS/PATH/target/release/promoshot-mcp \
  --workspace /ABS/PATH/Promo --root /ABS/PATH/Promo
grok inspect   # confirms the server registered

# Docker — the host needs nothing but docker (details below)
docker build -t promoshot-mcp .
# then command: docker, args: ["run","-i","--rm","-v","/ABS/PATH/Promo:/projects","promoshot-mcp"]

3. Skill (the workflow)

Same file everywhere: skill/SKILL.md.

REPO=https://github.com/GarAlex/promoshot
git clone --depth 1 $REPO /tmp/promoshot

# Claude Code (Grok Build also scans this folder)
mkdir -p ~/.claude/skills/promoshot
cp /tmp/promoshot/skill/SKILL.md ~/.claude/skills/promoshot/SKILL.md

# Grok Build explicit path
mkdir -p ~/.grok/skills/promoshot
cp /tmp/promoshot/skill/SKILL.md ~/.grok/skills/promoshot/SKILL.md

# OpenAI Codex / many others
mkdir -p ~/.agents/skills/promoshot
cp /tmp/promoshot/skill/SKILL.md ~/.agents/skills/promoshot/SKILL.md

# Cursor project (in the repo the user is editing, not this engine repo)
mkdir -p .cursor/rules
cp /tmp/promoshot/skill/SKILL.md .cursor/rules/promoshot.md
# or: mkdir -p .agents/skills/promoshot && cp SKILL.md there

Any agent that reads instructions can be handed the file directly; it assumes only these tools (or the CLI).

4. Verify — ask the agent for a render:

Render examples/ProductCard.promo to a still at 3s.

One promo_validate, one promo_render_still, and a device-framed app demo comes back as a path. From there, "make me a promo for " is the loop the skill teaches.

The tools

Tools: promo_schema (authoring subset + four validated recipes; promo_schema_full is the whole format; promo_schema_types is the format as a generated, types-only JSON Schema — also checked in at docs/promo.schema.json for $schema editor autocomplete), promo_validate, promo_inspect (each layer listed with its id — the handle the editing tools take), promo_render_still, promo_render_frames, promo_render_video, promo_render_gif, promo_workspace; the senses — promo_media_probe, promo_media_filmstrip (a contact sheet of a SOURCE clip, times per cell), promo_media_silences (silence spans and their inverse) and promo_media_scenes (scene cuts and the shots between them), so an agent knows what footage holds before composing with it; the editor trio, promo_init, promo_upsert_layer and promo_upsert_keyframe: create a project, add image/video/caption layers with placements, then animate — a second placement keyframe is a push-in, viewport keyframes a Ken Burns; your short ids are used verbatim, unnamed ones get canonical UUIDs, pixel sizes are stamped, and the composition keeps covering its layers. Device frames bake headless too — the same slab the apps draw. promo_slideshow is the wizard: pictures and clips in, a complete classic, carousel or store-listing show out, a caption on any slide becoming a layer that lives with its picture. promo_voices lists a provider's voices and promo_speak synthesizes narration with the person's own provider key, reusing unchanged text by receipt. The authoring tools answer with an inline thumbnail of the composition, so a misplaced layer is caught at the moment it happens. The tools write ordinary metadata.json through the format's own parser — the schema stays the source of truth, and hand-editing remains first-class. Renders default their output into the project's Exports/ folder and return the path written, never the bytes.

Flags, all optional: --workspace <dir> (where promo_workspace points; else $PROMOSHOT_WORKSPACE, else the XDG data dir), --root <dir> (refuse projects outside this tree), --promo <path>.

Narration keys

Narration spends the person's own provider account, and the key never passes through the agent: no tool takes one, none shows one. Register it once in the OS keyring — macOS Keychain, the Secret Service on Linux (GNOME Keyring, KWallet), the Credential Manager on Windows:

promoshot-mcp key set openai        # reads the key from stdin: paste, then Ctrl-D
promoshot-mcp key status            # where each provider's key comes from, never the key
promoshot-mcp key remove openai

Providers: openai, elevenlabs, google. The key is read from stdin so it lands in no shell history, no config file and no argument list.

Where there is no keyring — the Docker image, a CI runner — the key is read from a secrets file, the way Docker, Kubernetes and CI systems hand secrets over: /run/secrets/OPENAI_API_KEY (likewise ELEVENLABS_API_KEY, GOOGLE_API_KEY), or the path named by OPENAI_API_KEY_FILE. A mode-0400 file, never an environment variable that docker inspect and every same-user process can read:

docker run -i --rm \
  -v "$HOME/.secrets/openai:/run/secrets/OPENAI_API_KEY:ro" \
  -v /path/to/your/projects:/projects promoshot-mcp

An agent can ask before it plans: promo_speak with {"check": true} spends nothing and reports, per provider, whether a key is present and what a real call would synthesize. A real call checks every pending narration's key before buying anything, and writes each receipt back the moment it is paid for, so a failure part-way never makes the next call pay twice. Keys travel in request headers, never URLs, and nothing logs them.

Docker

The image is the whole render environment — server, CLI, ffmpeg, a software Vulkan and the fonts — so a client needs nothing on the host:

docker build -t promoshot-mcp .

{
  "mcpServers": {
    "promoshot": {
      "command": "docker",
      "args": ["run", "-i", "--rm",
               "-v", "/path/to/your/projects:/projects",
               "promoshot-mcp"]
    }
  }
}

Projects live under the mount; promo_workspace answers /projects. All the examples are baked in, so the image proves itself with no mount at all — render ProductCard.promo first; the device-framed app demo is the one that teaches the product-promo path. server.json is the MCP Registry manifest (io.github.GarAlex/promoshot) for the published image (ghcr.io/garalex/promoshot-mcp). GitHub's MCP Registry consumes that feed after mcp-publisher publish.

mcp-name: io.github.GarAlex/promoshot

The skill is drift-tested: a test pins it to the server's actual tool list, so it cannot teach tools that do not exist.

The Mac app carries its own MCP server (Settings → Automation) sharing the core tool names, plus app-only abilities — opening the editor, speech synthesis. The authoring pair, the senses and the types schema are headless-first.

What a session looks like — three requests in, a validated project and a rendered frame out (the frame at the top of this page was made exactly this way):

{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-06-18"}}
{"jsonrpc":"2.0","method":"notifications/initialized"}
{"jsonrpc":"2.0","id":2,"method":"tools/call","params":{"name":"promo_validate","arguments":{"project":"examples/LinuxSmoke.promo"}}}
{"jsonrpc":"2.0","id":3,"method":"tools/call","params":{"name":"promo_render_still","arguments":{"project":"examples/LinuxSmoke.promo","time":5.5}}}

{"id":2,"result":{"content":[{"type":"text","text":"ok — nothing the renderer would quietly correct"}]}}
{"id":3,"result":{"content":[{"type":"text","text":"wrote examples/LinuxSmoke.promo/Exports/still-5.5s.png (1280x720 at 5.50s)"}]}}

One engine, every platform

The same project rendered on macOS (Metal, VideoToolbox) and on a bare Linux container (lavapipe software Vulkan, no GPU; ffmpeg) — SSIM 0.983 over the full 240-frame video. The visible difference is the font: the caption asks the question, the two frames answer it.

Try it yourself — examples/ holds one runnable project per promo_schema recipe (each metadata.json IS its recipe, pinned by a test), from the device-framed product card to the 9:16 re-stamp — plus the kitchen-sink LinuxSmoke.promo:

promo video examples/ProductCard.promo --out card.mp4

Authoring a project

Start with promo schema. The short version: a project folder holds metadata.json and Resources/; ids are unique strings (short mnemonics are fine — apps mint UUIDs on adoption); layers place resources on a timeline with keyframes (hold-then-ease), placement rules, transitions and palette-named colours (@accent). Validate before rendering — the validator names what the renderer would silently correct, undefined colour names included.

mkdir -p Demo.promo/Resources
# write Demo.promo/metadata.json, copy media into Resources/
promo validate Demo.promo && promo still Demo.promo --out look.png --time 1

Or let the MCP server spend the boilerplate (promo_init, promo_upsert_layer), and give your editor autocomplete by pointing "$schema" at docs/promo.schema.json.

Invariants and plans

• SPECS.md — the invariants the tests pin.

License

Apache-2.0. The PromoShot applications built on this engine are separate, proprietary products.

Proxies for long sources

promo proxy <project> builds a tier-1 proxy (960 px long edge, every frame a keyframe) for each video resource, in a cache outside the package ($PROMO_PROXY_DIR, else the platform cache directory under promoshot/proxies). still, frames, gif and video take --proxy auto|on|off: auto (default) reads a built proxy when the output's long edge fits it, on builds missing proxies first, off reads the source — and a full-size render always does. The MCP tools take the same proxy argument; promo_proxy builds them.

Markers and chapters

A project may carry markers — named moments on the output timeline. kind: "chapter" markers are written into an exported mp4's chapter list (a player's chapter menu); inspect lists them all.

Audio effects

A video or audio resource may carry audioEffects — normalize (loudness to a target LUFS), compressor and one-band eq entries, applied in order before the mix in every render the core makes. The apps' exports take the same mix; their live preview plays the resource dry.

Chroma key

A video or image layer may carry chromaKey — a colour, a tolerance and a softness: the plate becomes transparent before the layer's grade, border and mask, in the compositor, so a green-screen clip composes over anything on every host alike.

Models

A resource of kind model is a glTF 2.0 binary (.glb) in Resources/; a layer of kind model draws it through a PBR-lite pass into a texture at the layer's size, and from there it is a picture like any other: placement, opacity, transitions, masks, effects and the contact shadow all apply. Keyframes carry a camera (yaw, pitch, roll, distance in bounds radii, fov) and a light; materials on the resource bind a slot name to a colour — a palette name works, so @accent re-skins the body with the theme — and, in the object form, to a finish: metallic and roughness (each 0…1) over the file's own, so one body is chrome in this project and matte in the next (rung 32) — or, better, to a finish WORD (rung 44): chrome, brushed, anodized, gloss, satin, matte, rubber, ceramic, lacquer, paper, glass, frosted, each expanded by the engine into the numbers, the coat, the grain, the transmission and the refraction it stands for, so nobody levels a reflection by hand; on a screen the word is the coat over the picture, and glass on a stage bends the bodies behind it. Lighting defaults come from the theme; a scene environment (studio, sunset, night; rung 35 — or, rung 46, a resourceID naming a panorama in the project, a picture of the world the bodies mirror) is what metals mirror; a file's normal map and metallic-roughness texture are honoured. Rung 29. Built-in device bodies (phone, tablet, laptop; promo device) ship as generated .glb files with Body and Screen slots, so the device shot is a model too. A model can also be a recipe the engine builds at load instead of a file — text as a body first: real type in the 3D world with Face and Side slots, lit and finished like any body (rung 34); a device body; and a body of PARTS — boxes, spheres, cylinders, tori, a lathe, an extrude, each under a slot, placed by position, rotation and scale — the 3D counterpart of a drawing, authored the way an SVG is (rung 37). Layers naming the same stage draw through one camera into one depth buffer, models at their depth and pictures as billboards, the first member's placement carrying the whole scene (rung 30). A stage can also be one layer of kind stage holding its members, the camera and light on its own keyframes (rung 33) — the same picture, with the stage's ownership written down. A stage's floor word (rung 45) — matte, satin, glossy, mirror — puts a plane under the lowest body that catches the key light's shadow, the darkening where a body touches, and the stage mirrored in it, blurred less and less; whatever lies beneath the stage layer shows through, so the table is the project's own background. The light's keyframes move the shadow; the floor stays.

A picture worn by a body

A slot's picture is a screen by default: unlit, fitted, what a screenshot on a phone wants. "mode": "surface" on the binding wears it instead — the image or video becomes the slot's colour under the light and the finish, tiled by repeat and shifted by offset, the slot's own colour showing through where the picture is transparent — so a label sits on a vase, a print on a box, and a video plays on a glossy wall that the key light and the environment still shade. Rung 38.

Particles

A resource of kind particles is a recipe, not a file — an emitter, a rate or a burst, life, speed, gravity, wind, drag, turbulence, size and colour over life, a shape — played by a drawing layer. Every particle is a closed-form function of its birth time and the seed, so any frame renders alone and identically on every host. Rung 36.

A path resource can carry a route in the stage (rung 40): 3D points in stage radii that a member's or a camera's motionPath follows, fitted between two keyframes exactly as the 2D motion path is, with a camera target — the centre, ahead, a member or a point — saying where it looks on the way. A spiral that keeps looking inward is one route and one keyframe.

Particles in a stage are a morph (rung 39): the recipe names two bodies, samples the first's surface, and as a drawing member's progress keyframe ramps from 0 to 1 the points fly out and gather on the second body — a cube bursts into points that settle into a word. A parts box with faces: true has six slots, one picture per side, which is what such a cube is made of.

Text with a side

Legacy: the caption depth below is the flat compositor's 2.5D. A title with a real side is a text body (rung 34) standing in a stage; the validator names the old form. It still renders.

A caption style may carry depth: copies of the words stacked under the face, each a little further along and darker, so the type reads as solid letters with a side — the classic extrusion, pure 2D, lit by choosing the offset. A reveal extrudes each arriving piece the same way. tiltX / tiltY keyframes on a caption lean it in perspective, on the same camera the device frames use, and the side leans with the face. A reveal's flip, tumble and slide modes bring each word in on its own axes — kinetic type from one rule, no keyframes.

Follow the pointer

A video the Mac recorder made carries pointer, where the pointer went and where it clicked, in the recording's own time and coordinates. A layer showing it may say follow: its viewport becomes a window 1/zoom of the source that follows the smoothed pointer, and each click draws a ring that grows and fades. A rule, not keyframes: re-trim the recording and it stays true, on every host alike.

Image effects

A layer may carry effects: a blur (round, or directional along a blurAngle), a glow of its bright parts, a vignette toward its own corners, film grain and an unsharp sharpen, each on the layer's own pixels in the compositor. Blur, glow and vignette are keyframe tracks too, so a focus pull or a glow that pulses ramps like the grade does. Five transitions ride the same passes — blurDissolve, zoom, flash, glitch and dip — beside the fade, wipe, slide, push and scale that were there, at a layer's edges and at a resource swap alike. A video layer's swap may name a composition (rung 47): the takeover, the next film arriving through any of those cuts where its sourceTime says, or where its clock already is. The same keyframes carry the consumer's transport for anything with a clock — a video, an audio, a composition, a sprite: sourceTime seeks it, playback pauses and resumes it, and its sound follows.

Looks from a .cube

A resource of kind lut is a .cube file in Resources/; a layer's adjustments.lutResourceID (with lutAmount) applies it in the compositor after the layer's own grade — a trilinear lookup on every host alike.

ProRes and alpha

promo video … --codec prores422|prores4444 --out x.mov writes ProRes; --alpha renders the project over nothing and keeps the frames' alpha in a ProRes 4444 (--alpha on still/frames gives transparent PNGs). Sources that carry alpha (ProRes 4444, WebM with alpha, PNG sequences) decode premultiplied and compose with their transparency.