HappyHorse Image-to-Video

POST /api/v1/services/aigc/video-generation/video-synthesis — generate video from a first-frame image

The HappyHorse image-to-video model animates a first-frame image, steered by an optional text description.

Models

Model	Notes
`happyhorse-1.1-i2v`	Generation 1.1
`happyhorse-1.0-i2v`	Generation 1.0
`happyhorse-1.0-i2v-20260618`	Generation 1.0, 20260618 snapshot

Create a job

POST/api/v1/services/aigc/video-generation/video-synthesis

curl https://api.modelsite.ai/api/v1/services/aigc/video-generation/video-synthesis \
  -H "Authorization: Bearer $MODELSITE_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "model": "happyhorse-1.1-i2v",
    "input": {
      "prompt": "A cat running across a meadow",
      "media": [
        { "type": "first_frame", "url": "https://example.com/cat.png" }
      ]
    },
    "parameters": { "resolution": "720P", "duration": 5 }
  }'

Request body

Field	Type	Notes
`model`	string (required)	See the table above
`input.prompt`	string (optional)	Describes the intended motion. CJK counts as 2, everything else as 1, budget 5000
`input.media`	array (required)	Exactly one `first_frame` entry: `{"type": "first_frame", "url": "..."}`. URL or `data:` Base64 both work
`parameters`	object (optional)	Generation knobs, below

parameters

Parameter	Type	Notes
`resolution`	string	`480P` / `720P` / `1080P` (default). Sellable tiers follow the price configuration. Output aspect ratio follows the first frame
`duration`	integer	`[3, 15]`, default 5
`watermark`	boolean	Defaults to `true` ("Happy Horse" stamp); pass `false` explicitly to opt out
`seed`	integer	`[0, 2147483647]`
`negative_prompt`	string	Negative prompt

Image-to-video does not accept parameters.ratio — the output aspect ratio follows the first frame, and sending one is an InvalidParameter error.

First-frame requirements: JPEG / JPG / PNG / WEBP, both sides ≥300px, aspect ratio 1:2.5–2.5:1, ≤20MB.

Polling and result

GET/api/v1/tasks/{task_id}

curl "https://api.modelsite.ai/api/v1/tasks/$TASK_ID" \
  -H "Authorization: Bearer $MODELSITE_API_KEY"

Response fields

Field	Meaning
`output.task_id`	Job ID (same value returned at creation)
`output.task_status`	`PENDING` queued / `RUNNING` processing / `SUCCEEDED` done / `FAILED` failed
`output.video_url`	The generated video URL — only on `SUCCEEDED`; download promptly
`output.code` / `output.message`	Present only on failure, with the reason
`usage`	Usage stats (duration, resolution tier, …); counted only on success
`request_id`	Unique request ID — include it when reporting issues

Status flow: PENDING → RUNNING → SUCCEEDED / FAILED.

Billing

Billed by actual generated seconds; the resolution tier affects the rate; failed jobs are not billed. Rates on the Models page.

Error handling

Creation-time errors return {"code": "...", "message": "..."}; mid-job failures surface through the poll's output.code / output.message. General error codes: Errors.