add-model-04-port-vae - SKILL.md Agent Skill

name: add-model-04-port-vae description: Use during /add-model Phase 4 or Phase 6 to prototype or parity-debug one FastVideo-native VAE component.

Add Model Port VAE

Goal

Prototype or parity-debug one VAE or autoencoder in FastVideo-native code. This skill covers video, image, and audio VAEs.

Inputs

Follow ../add-model/shared/component_skill_common.md and require the complete packet from ../add-model/contracts/component_context.md.

VAE-specific packet fields:

component: VAE or autoencoder name.
parity_test: tests/local_tests/vaes/test_<family>_<component>_parity.py.
weights: converted VAE dir, HF subfolder, or local official path.
target_files: fastvideo/models/vaes/<arch_or_family>.py and fastvideo/configs/models/vaes/<arch_or_family>.py.

Modes

Use the common prototype and parity-debug modes from ../add-model/shared/component_skill_common.md.

VAE-specific prototype concerns include latent normalization, stochastic posterior behavior, tiling incompatibility, temporal/spatial/audio layout, and decode output containers.

Reuse Proof

Apply the shared reuse proof. VAE-specific comparison must include latent layout, temporal/spatial/audio compression, scaling factor, mean/std normalization, posterior behavior, encode/decode output objects, tiling flags, and cropping.

Existing FastVideo Patterns

Shared tiling wrapper: fastvideo/models/vaes/common.py::ParallelTiledVAE.
Config bases: VAEConfig and VAEArchConfig in fastvideo/configs/models/vaes/base.py.
Use the matching VAE config bucket. Wrong bucket inheritance can typecheck but fail during pipeline wiring.
Config export: add the config to fastvideo/configs/models/vaes/__init__.py.
Registry discovery: set EntryClass = <ClassName> in the model file.
Loader path: VAE loaders resolve _class_name through ModelRegistry and load converted component weights from the VAE subdir.
Reference examples: oobleck.py, autoencoder_kl.py, wanvae.py, ltx2vae.py, and gamecraftvae.py.
Layer guidance: fastvideo/layers/AGENTS.md.

Implementation Rules

Name reusable VAE architectures by architecture (oobleck.py, autoencoder_kl.py); name family-specific VAEs by family.
Match official encode/decode contracts exactly: input layout, latent layout, temporal/spatial/audio compression, scaling factor, mean/std normalization, posterior sampling behavior, decode output object, and frame/sample cropping.
Compare deterministic outputs in parity: decode outputs, encode mean/mode, or round-trip tensors. Do not compare stochastic samples unless the RNG path is explicitly controlled.
Use FastVideo tiling only when it preserves official numerics for the tested shape; disable it in config for audio or unsupported dimensions.
Put architecture constants on VAEArchConfig; put load_encoder, load_decoder, tiling, dtype, and pretrained path fields on VAEConfig.
Follow the production import boundary in ../add-model/shared/common_rules.md.

Prototype Checks

Follow the shared prototype success criteria.

Parity-Debug Loop

Run the shared parity-debug loop. The component test command is:

pytest <parity_test> -v -s

For numerical drift, check normalization, latent scaling, posterior mode vs sample, channel order, and temporal/spatial/audio cropping before changing layers.

Escape Hatches

Follow ../add-model/shared/common_rules.md and the component-specific guidance in ../add-model/shared/component_skill_common.md. VAE-specific ask cases include dropping an encode/decode path, accepting an unsupported private op, or choosing between incompatible official VAE definitions.

Handoff

Return ../add-model/contracts/component_skill_handoff.md following the common handoff rules in ../add-model/shared/component_skill_common.md.