@altexo/ai-gen

Direct-API scripts for AI image and video generation. Calls Nano Banana Pro (image), OpenAI gpt-image-1 (image), Veo 3.1 (video), and Kling 3 (video) over their native APIs and writes deterministic outputs into out/<project>/YYYY-MM-DD_HHMM_<slug>_<model>/ with a manifest.json reproducibility receipt.

It's a cheaper, reproducible alternative to canvas-style aggregators when you run the same template many times — every call is scripted from a small YAML file, so a shot is re-runnable and diff-able instead of hand-clicked.

Release notes live in CHANGELOG.md.

Install

npm install @altexo/ai-gen

Or work from a clone:

git clone https://github.com/xorsnn/altexo.git
cd altexo && npm install
cd packages/ai-gen
cp .env.example .env     # fill in your keys

Node >= 20.3.

Quickstart

# image (Nano Banana)
npm run image -- prompts/example.image.yaml

# image (OpenAI gpt-image-1) — same YAML, different engine
npm run openai -- prompts/example.image.yaml

# video (Veo)
npm run veo -- prompts/example.veo.yaml

# video (Kling, official API)
npm run kling -- prompts/example.kling.yaml

# image -> video pipeline
npm run pipeline -- prompts/example.pipeline.yaml

Outputs land in out/<project>/YYYY-MM-DD_HHMM_<slug>_<modelAlias>/. The project subfolder groups every asset for one job side-by-side; the model alias in the suffix keeps comparisons (e.g. ..._myshot_kling-pro vs ..._myshot_veo-fast) scannable at a glance. Every prompt YAML must declare a project: field — the scripts refuse to run without it (see prompts/_schema.md). out/ is gitignored.

Library usage

The package is embeddable — import from the package root (deep src/* imports are not part of the contract). TypeScript declarations ship with the package. Importing loads no .env and never mutates process.env (only the CLI entry points read the package-local .env). The one thing that happens at import time is a synchronous read of the packaged model-registry JSON — so a bad AI_GEN_MODELS_CONFIG path throws immediately instead of mispricing later.

import { generateImage, MissingKeyError, SafetyBlockError } from '@altexo/ai-gen';

const { images, modelId, costEstimate } = await generateImage({
  prompt: 'a lighthouse at dusk, volumetric fog',
  aspect: '9:16',
  references: ['/tmp/parent-frame.png'], // read from disk — server-trusted paths only
  numberOfImages: 3,
  apiKey: userKey,                        // per-call; falls back to GEMINI_API_KEY
  signal: controller.signal,              // optional AbortSignal
  timeoutMs: 120_000,                     // default; 0 disables the bound
});
// images: [{ mimeType, data: Buffer }]

The library throws, never calls process.exit — safe to embed in a server. generateImage failures carry a stable code for programmatic handling: missing-key (no/invalid key), invalid-input (unknown model, unreadable reference, bad count — deterministic, don't retry unchanged), safety-block (model returned zero images — rephrase and retry), rate-limit (HTTP 429 — back off), network (transport/5xx — retry), unknown (anything else, wrapped as AiGenError). Caller aborts and timeouts surface unwrapped (err.name === 'AbortError' | 'TimeoutError') — the library recovers the distinction even though the underlying SDK drops abort reasons.

Trust boundaries: references paths are read from disk and sent to the provider — never wire raw user input into them (the reads are bounded by the same abort/timeout as the provider call). saveImages(images, outDir, prefix) creates outDir if missing; outDir must be server-trusted and prefix must be a bare file-name fragment (path separators are rejected). File names are deterministic, so a reused outDir fails loudly (wx) instead of silently overwriting a sibling generation. saveImages filesystem failures are raw Node errors, not taxonomy errors, and all writes have settled before it returns or throws.

Next.js embedders: add serverExternalPackages: ['@altexo/ai-gen'] to next.config.js. The model registry is read from a packaged JSON at runtime via import.meta.url-relative paths, which breaks if the bundler inlines the package.

Also exported: saveImages, extractImages, MODELS, priceImage, priceVideo, estimateImageCost, classifyError, and the error classes. Off the surface until hardened to the same contract: the video generators (Veo, Kling) and the OpenAI image generator.

Configuration

The toolkit runs from config — nothing is hardcoded to a particular machine or repo.

API keys. The CLI loads .env if present — package-local when run from a clone, from your current directory when installed via npm/npx (that's where altexo-ai-gen init writes it). The library never loads .env — pass apiKey per call or set the env vars yourself. Values already in your shell environment take precedence. Required:

• GEMINI_API_KEY — Nano Banana + Veo — https://aistudio.google.com/apikey
• KLING_ACCESS_KEY + KLING_SECRET_KEY — Kling — https://app.klingai.com/global/dev/account
• OPENAI_API_KEY — gpt-image-1 (optional) — https://platform.openai.com/api-keys

See .env.example.

Model registry + pricing live in models.default.json (data, not code; src/models.js reads it). To change model IDs or prices without editing source, set AI_GEN_MODELS_CONFIG to a JSON file path (absolute, or relative to cwd). It layers per-model shallow replace: a model present in your override replaces the default entry wholesale, models you don't mention keep their defaults, and new aliases are added. A bad path throws — a misconfigured override surfaces immediately rather than silently mispricing.

// my-models.json — bump Kling Pro's price and swap its model id
{ "kling-pro": { "vendor": "kling", "id": "kling-v3.1", "mode": "pro",
                 "kind": "video", "pricing": { "5": 0.50, "10": 1.00 } } }

AI_GEN_MODELS_CONFIG=./my-models.json npm run kling -- prompts/example.kling.yaml

Output root. Defaults to the package's own out/ directory — that is ./out when you work from a clone's package root, but for npm/npx installs it lands inside the installed package copy. Set AI_GEN_OUT_ROOT (absolute, or relative to cwd) to write elsewhere — recommended for installed use.

Prompt files

YAML — see prompts/_schema.md for the full field reference. The prompts/example.*.yaml files are working samples for each generator.

Cost reference (per single generation, USD)

Native API list prices, from models.default.json:

| Model | Output | Native API | | ------------------- | ------------- | ---------: | | Nano Banana Pro 1K | image | $0.134 | | Nano Banana Pro 2K | image | $0.134 | | Nano Banana Pro 4K | image | $0.24 | | Nano Banana Flash | image | $0.039 | | gpt-image-1 (high) | image (2:3) | ~$0.25 | | Veo 3.1 (8s) | video + audio | $3.20 | | Veo 3.1 Fast (8s) | video + audio | $1.20 | | Kling 3 Master | video | ~$0.14/s | | Kling 3 Pro | video | ~$0.084/s | | Kling 3 Std | video | ~$0.042/s |

Aggregators that resell these models typically mark them up ~1.5–3× (and often gate them behind a subscription), which is the whole reason this calls the native APIs directly. Each run's manifest.json records the cost estimate. Prices approximate as of mid-2026 — verify against the providers' current pricing.

Kling 3 bills per second over a 3–15s clip (e.g. kling-pro: 5s ≈ $0.42, 10s ≈ $0.84, 15s ≈ $1.26); the per-second rates are derived from the legacy 5/10s points. kling-pro with audio: true doubles (2× audioMultiplier).

Model notes

Nano Banana Pro — src/nano-banana.js

• Model ID gemini-3-pro-image-preview (use nano-banana-flash → gemini-2.5-flash-image for cheaper drafts).
• SDK @google/genai, ai.models.generateContent({...}) with responseModalities: ['IMAGE'].
• Aspect ratios: 1:1, 2:3, 3:2, 3:4, 4:3, 4:5, 5:4, 9:16, 16:9, 21:9.
• Up to 14 reference images via references: — how you keep style/character consistent across a series.
• Outputs carry an invisible SynthID watermark.

Veo 3.1 — src/veo.js

• Model IDs veo-3.1-generate-preview or veo-3.1-fast-generate-preview (~3× cheaper).
• Same GEMINI_API_KEY. SDK ai.models.generateVideos({...}) returns a long-running op; the wrapper polls every 10s and downloads the MP4 (Veo URIs need the API key as a ?key= param to download).
• Length 4/6/8s. Native audio on by default (audio: false to disable).
• image_input: animates a still — the natural pairing with Nano Banana.
• A single video typically takes 1–4 minutes.

Kling 3 — src/kling.js

• Kuaishou's official international API at https://api.klingai.com.
• Auth: JWT (HS256) signed from KLING_ACCESS_KEY + KLING_SECRET_KEY; the wrapper mints a fresh 30-min token per call via jsonwebtoken.
• Model IDs are best-guess for Kling 3 — if you get invalid model_name, open the Kling dev console, trigger a working request, and copy the exact model_name from the Network tab into your AI_GEN_MODELS_CONFIG override.
• Length: Kling 3 (pro/std) is the integer range 3–15s (default 5); legacy tiers were 5/10. Allowed values are data-driven per model (models.default.json durations); the wrapper rejects an out-of-range length. image_input: is base64-encoded into the request (no upload step).
• Native audio on kling-pro: set audio: true for synced SFX / ambient — the wrapper sends the official Kling sound: "on" field. Pro tier only, single start frame only (not with image_tail), billed at the model's audioMultiplier (~2×). Other tiers are silent — pair with a music bed in your editor.
• Multi-shot (Kling v3): multi_shot: [{ prompt, seconds }] (≤6 shots) splits one clip into prompted segments; the seconds sum to the clip length (3–15). shot_type: customize honors the list, intelligence auto-storyboards. Good for a motion arc, not a hold-still beat. (lib: generateVideo({ multiShot, shotType }).)
• Reference subjects / elements (Kling v3): keep a character/object consistent across the clip. Build a reusable element with node scripts/gen-kling-element.js <name> <frontal.png> <refer1.png> [refer2 ...] (a frontal + 1–3 refer images), or inline via elements: [{name, description, images}]; then reference it in the prompt as <<<element_1>>> (max 3). lib: createElement() + generateVideo({ elementIds }).
• Base URL override: KLING_BASE_URL (the international host moved to api-singapore.klingai.com; the default api.klingai.com still resolves).
• Rate limits are stricter than Google's; keep calls sequential.

OpenAI gpt-image-1 — src/openai-image.js

• A second image engine, handy for A/B: feed the same prompt YAML to npm run openai and npm run image and compare gpt-image-1 against Nano Banana.
• Auth: OPENAI_API_KEY. Dependency-free raw fetch against the Images API; mirrors the nano-banana.js shape so the same save / out-dir plumbing is reused.
• Sizes are fixed: 1024x1536 (2:3), 1024x1024 (1:1), 1536x1024 (3:2). There is no true 9:16 — a 9:16 input maps to 1024x1536 and the manifest records the actual pixel size. quality: is low / medium / high (default high).

Pipeline — scripts/gen-pipeline.js

Chains Nano Banana → Veo or Kling in one call, so you get a high-fidelity hero frame instead of letting the video model hallucinate the first frame from text. See prompts/example.pipeline.yaml.

Reproducibility

out/<run>/manifest.json captures the project, prompt, model ID, params, timing, and cost estimate — everything needed to re-run a generation. Commit a manifest alongside an asset if you want a permanent record of how it was made.

License

MIT © Sergei Grigorev