# Hosted video generation

Request measured video through an approved host capability.

Use `runtime: "capability"` and `permissions.capabilities: ["video.generate"]`. Declare one text, script or brief prompt input, up to two `image` inputs for the first and last frame, and one video output. Every video model the app's own Blocks use is available — Seedance 2.0 (and Fast, Mini), Kling 3.0 Turbo, Wan 2.6 Flash, Veo 3.1 Lite, Vidu Q3 Turbo and Wan 2.7 — with their durations, resolutions, aspect ratios, image-to-video and first-and-last-frame modes (see [generation models](/docs/reference/generation-models)). Users pay with StillMade credits at StillMade's per-second price. The capability file is:

```json
{"schemaVersion":1,"operation":"video.generate","prompt":{"$input":"prompt"},
 "firstFrame":{"$input":"start"},"lastFrame":{"$input":"end"},
 "settings":{"model":"veo-3.1-lite","duration":6,"resolution":"720p","aspectRatio":"16:9","generateAudio":true},
 "negativePrompt":"blur","seed":7,"output":"video"}
```

`settings`, `firstFrame`, `lastFrame`, `negativePrompt` and `seed` are optional; each setting must be one the model accepts (Veo locks 1080p to 8 seconds; Wan 2.7 needs a first frame). Never include provider endpoints, keys, prices or payment. The run dialog preselects the Block's defaults and the user may change them before seeing the exact price. The invocation is `{operation:"video.generate",prompt}` plus `firstFrame`, `lastFrame`, `negativePrompt` and `seed` when declared; frames must be the user's own saved images. Public trials use their separately reviewed acquisition policy and never account BYOK.

The canonical output has `kind:"video"`, bounded `assetId`/`versionId`, a stored HTTPS or host media `url`, `mimeType:"video/mp4"`, measured `width`, `height`, `duration` in seconds and `bytes`. The host keeps the provider's MP4 byte-for-byte after measuring its container. SDK limits are 60 seconds, 256 MiB, at most 3,840 pixels on either axis and 8,294,400 pixels per frame. Validating this shape does not verify ownership or real video bytes; the host must inspect, store and verify them.

Fixtures use `kind:"video"`, `format:"mp4"` and explicit `minDuration`, `maxDuration`, `minBytes`, `maxBytes`, `minWidth`, `maxWidth`, `minHeight`, `maxHeight` bounds. See `packages/block-sdk/video-generation-example.js`. Provider fixtures require approval; they are not deterministic equality tests. `validateGeneratedVideoReference`, `defaultCapabilityExpectations` and `validateCapabilityResult` are available through the SDK. Media receipts bind the owner, run, invocation, storage key and SHA-256 digest to the complete output reference. Guest code cannot issue those receipts.

A host advertises only enabled operations. A valid package does not imply every deployment has video generation configured; unavailable hosts must reject it before billing or dispatch. Public video results use the same private media/claim lifecycle as other trial outputs and are retained when continuing in an account.


### Authored state migration routes

A new JavaScript Block release can optionally declare `manifest.state.migrations`
for explicit upgrades of its Step memory. A route's `fromVersion` is an older
positive state schema version; its destination is the enclosing `state.version`.
For example, a declaration for state version 2 can contain:

```json
"migrations": [{
  "fromVersion": 1,
  "operations": [
    { "op": "rename", "from": "count", "to": "completed" },
    { "op": "default", "key": "labels", "value": [] },
    { "op": "remove", "key": "temporary" }
  ]
}]
```

Operations run in order on safe ASCII top-level field names. Rename requires an
existing source and absent destination; default writes only if absent; remove
requires the field to exist. Nested values remain intact. There are at most 16
distinct older-version routes and 64 operations per route. Combined declarations
and every intermediate state each fit within 64 KiB. An empty operation list
explicitly advances only the schema version. There is no implicit chaining,
downgrade, deep-path transformation, expression evaluation or code execution.

The portable SDK exports `validateStateMigrations(stateDeclaration)`,
`stateMigrationRoute(manifest, fromVersion)`, and
`migrateBlockState(previousManifest, nextManifest, savedState)`. The last returns
`{state, operations, fromVersion, toVersion}` without modifying its inputs. Both
manifests must describe the same JavaScript Block identity, with valid state
contracts. Matching state versions use an identity transfer; changed versions
require an exact direct route. Runtime execution does not invoke migrations.

Migration declarations change package source: publish a new immutable Block
release and keep its fixtures on the target schema. Do not guess existing state
fields or reset user memory. In StillMade, owners review exact archived/current
source pins, operations and before/after memory, then explicitly apply. The host
rechecks account/project/source/state, retains rollback history and invalidates
downstream results. External hosts must provide equivalent ownership, source
verification, approval and rollback boundaries before accepting the result.