Vfx Usd

Vfx Usd

Context: $ARGUMENTS

Quick start

• Convert between .usda / .usdc / .usdz: -> Step 1 (usd.py cat)
• Inspect a stage hierarchy: -> Step 2 (usd.py info)
• Validate for delivery (Apple .usdz, studio pipeline): -> Step 3 (usd.py validate)
• Render a frame sequence from a stage: -> Step 4 (usd.py record)
• Pack a folder of assets into .usdz: -> Step 5 (usd.py zip)
• Diff two stages: -> Step 6 (usd.py diff)
• Resolve an asset path: -> Step 7 (usd.py resolve)
• Interactive viewer: -> Step 8 (usd.py view)
• Assemble value clips: -> Step 9 (usd.py stitch-clips)

When to use

• User mentions Pixar USD, OpenUSD, .usd/.usda/.usdc/.usdz files, Hydra rendering, AR asset export.
• Validating a USD for Apple Quick Look AR delivery (.usdz).
• Converting between ASCII (.usda) and binary (.usdc) crate forms.
• Rendering an offline image sequence from a camera prim.
• Inspecting composition arcs (sublayer/reference/payload/inherit/specialize/variantSet).

Step 1 — Convert between USD formats

uv run ${CLAUDE_SKILL_DIR}/scripts/usd.py cat --in scene.usdc --out scene.usda

Under the hood:

usdcat scene.usdc -o scene.usda

Use --flatten to resolve all composition arcs into a single layer (baking references/payloads/variants into the output):

uv run ${CLAUDE_SKILL_DIR}/scripts/usd.py cat --in scene.usda --flatten --out scene_flat.usda

Format is auto-detected from the output extension: .usda -> ASCII, .usdc -> crate binary, .usdz -> package.

Step 2 — Inspect a stage

Hierarchy + attribute summary:

uv run ${CLAUDE_SKILL_DIR}/scripts/usd.py info scene.usda

Runs both:

usdtree scene.usda        # prim hierarchy
usdchecker scene.usda     # schema + packaging validation

Step 3 — Validate

uv run ${CLAUDE_SKILL_DIR}/scripts/usd.py validate scene.usdz

Expands to:

usdchecker --strict scene.usdz

For Apple AR Quick Look .usdz delivery, add --arkit:

uv run ${CLAUDE_SKILL_DIR}/scripts/usd.py validate --arkit model.usdz
# -> usdchecker --arkit --strict model.usdz

Step 4 — Offline render (Hydra)

Render N frames through a named camera prim, write to PNG sequence:

uv run ${CLAUDE_SKILL_DIR}/scripts/usd.py record \
  --in scene.usda \
  --camera /World/MainCam \
  --out render.####.png \
  --frames 1-240

Expands to:

usdrecord --camera /World/MainCam --frames 1:240 scene.usda render.####.png

Options: --imageWidth 1920, --renderer Storm|Embree|Arnold|Karma|RenderMan.

Step 5 — Zip / unzip a .usdz package

Pack a folder (root layer + referenced textures) into .usdz:

uv run ${CLAUDE_SKILL_DIR}/scripts/usd.py zip --dir ./asset/ --out asset.usdz

Extract contents:

uv run ${CLAUDE_SKILL_DIR}/scripts/usd.py unzip --in asset.usdz --dest ./asset/

Under the hood: usdzip, or on extract unzip / Python's zipfile (.usdz is just a zip).

Step 6 — Diff two stages

uv run ${CLAUDE_SKILL_DIR}/scripts/usd.py diff a.usda b.usda

Expands to usddiff a.usda b.usda. Structural diff — compares opinions by spec path, not line-by-line text.

Step 7 — Resolve an asset path

uv run ${CLAUDE_SKILL_DIR}/scripts/usd.py resolve "./textures/diffuse.<UDIM>.png"

Expands to usdresolve "./textures/diffuse.<UDIM>.png". Honors the current PXR_PLUGINPATH_NAME / USD_RESOLVER configuration. Useful for verifying that asset path templates resolve correctly in your pipeline.

Step 8 — Interactive viewer

Launch usdview on a stage:

uv run ${CLAUDE_SKILL_DIR}/scripts/usd.py view scene.usda

Requires Qt/PySide display; blocks until you quit. Skip on headless CI.

Step 9 — Stitch value clips

Animated "value clips" decouple per-frame layer swaps from the root layer. Build a manifest:

uv run ${CLAUDE_SKILL_DIR}/scripts/usd.py stitch-clips \
  --clips-dir ./clips/ \
  --topology topology.usd \
  --out manifest.usd

Expands to usdstitchclips --clipPath /Set --templatePath ./clips/frame.####.usd --startTimeCode 1 --endTimeCode 240 --out manifest.usd.

Gotchas

• Canonical docs live at https://openusd.org/release/, NOT /docs/. The /docs/ path returns 404. Pages you care about: /release/index.html, /release/intro.html, /release/glossary.html, /release/toolset.html, /release/tut_usd_tutorials.html. Quickstart PDF at /files/USD_Quickstart_Guide.pdf.
• Only four file extensions are canonical: .usd (generic — auto-picks crate or ASCII at read time), .usda (explicitly ASCII), .usdc (crate binary), .usdz (zip package). .usdnc is NOT a standard Pixar extension — don't recommend it.
• Composition arcs have a strict strength order: LIVRPS Local > Inherits > VariantSets > References > Payloads > Specializes. Stronger opinions override weaker ones. This is the most common pipeline footgun ("my edit isn't showing up" = there's a stronger opinion elsewhere).
• .usdz is just a ZIP with zero compression and specific alignment. The alignment is what usdzip does that plain zip cannot — do NOT build .usdz with plain zip, Quick Look will reject it.
• Apple's --arkit validator is stricter than default. Rejects PBR textures outside 8-bit range, requires triangulated meshes, limits shader support to UsdPreviewSurface. Always re-validate with --arkit before Apple submission.
• Tool list verified from openusd.org/release/toolset.html: usdcat, usdview, usdedit, usdzip, usdrecord, usdresolve, usdtree, usdchecker, usddiff, usdstitch, usdstitchclips, usdGenSchema, usdgenschemafromsdr. No "usdconv" or "usdexport" — those are NOT official tools.
• Schema docs split between user-guides and Doxygen API: UsdLux, UsdMedia, UsdRender, UsdUI, UsdVol have TOCs on /release/. UsdGeom, UsdShade, UsdSkel, UsdPhysics only have API pages like /release/api/usd_geom_page_front.html. Read references/schemas.md for one-liner summaries.
• usdview requires a Qt display. Won't work in headless CI; use usdrecord for offline render instead.
• Crate .usdc is version-stamped. A .usdc written by USD 24.x may fail to load on 23.x. Convert to .usda for forward-compat or ship the matching USD runtime.
• References vs Payloads: References are always loaded; Payloads are loaded on demand (stage.Load() / stage.Unload()). Use Payloads for heavy environment/city models. Don't mix them up — the loading semantics differ.

Examples

Example 1: "Convert a binary crate to ASCII for git diffs"

uv run ${CLAUDE_SKILL_DIR}/scripts/usd.py cat --in scene.usdc --out scene.usda

Example 2: "Validate this .usdz for Apple Quick Look"

uv run ${CLAUDE_SKILL_DIR}/scripts/usd.py validate --arkit model.usdz

Example 3: "Render frames 1-120 from the hero camera"

uv run ${CLAUDE_SKILL_DIR}/scripts/usd.py record \
  --in shot.usda --camera /Render/Cameras/hero \
  --frames 1-120 --out shot.####.png \
  --imageWidth 1920 --renderer Storm

Example 4: "Pack this asset folder into a shareable .usdz"

uv run ${CLAUDE_SKILL_DIR}/scripts/usd.py zip --dir ./hero_prop/ --out hero_prop.usdz
uv run ${CLAUDE_SKILL_DIR}/scripts/usd.py validate --arkit hero_prop.usdz

Example 5: "Flatten all composition into one file for a hand-off"

uv run ${CLAUDE_SKILL_DIR}/scripts/usd.py cat --in shot.usda --flatten --out shot_flat.usda

Troubleshooting

Error: usdcat: command not found

Cause: USD runtime isn't installed / not on PATH. Solution: Install via NVIDIA's build, brew install usd-core, pip install usd-core (limited Python bindings), or build from source at github.com/PixarAnimationStudios/OpenUSD.

Error: usdchecker --arkit FAILED

Cause: Apple-specific constraint (often non-triangulated mesh, missing UsdPreviewSurface, wrong texture color space, non-1-meter scale). Solution: Read the error; common fixes: triangulate in DCC before export, convert all shaders to UsdPreviewSurface, embed textures, set metersPerUnit=1.

.usdz opens in finder but not Quick Look

Cause: Built with plain zip (wrong alignment) or includes a directory entry. Solution: Rebuild with usdzip, not zip. Don't include __MACOSX/ or .DS_Store.

Error: Layer version too new

Cause: .usdc written by a newer USD runtime than the reader. Solution: Convert sender-side: usdcat new.usdc -o old.usda. Or upgrade reader.

My override isn't showing up

Cause: Stronger opinion exists up the LIVRPS chain. Solution: Use usdview → Composition tab, or usd.py info, to find who's "winning". Often a variantSet or specializes arc is overriding your layer.

usdrecord hangs on first frame

Cause: Hydra renderer loading plugins. Some renderers (Arnold) take 10-30s on first invocation. Solution: Wait. Pre-warm by rendering a tiny scene first, or switch to Storm (--renderer Storm) for speed.

Reference docs

• Core concepts cheatsheet (Stage / Layer / Prim / Attribute / Relationship / Composition Arcs / LIVRPS) -> [references/concepts.md]
• Schema one-liners (UsdGeom / UsdLux / UsdShade / UsdSkel / UsdPhysics / UsdMedia / UsdRender / UsdVol / UsdUI) -> [references/schemas.md]