---
title: "Select a preview source on a vision mixer block."
method: PUT
path: "/api/flows/{flow_id}/blocks/{block_id}/preview"
tags: ["flows"]
---

# Select a preview source on a vision mixer block.

`PUT /api/flows/{flow_id}/blocks/{block_id}/preview`

## Path parameters

- `flow_id` string, required
- `block_id` string, required

## Request body

- SelectPreviewRequest — Request to select a preview source on a vision mixer block.
  - `source` union, required — A source that can be assigned to PGM or PVW. JSON encoding is externally tagged: `{"input": 5}` or `{"pip": 1}`. The [`FromStr`] / [`fmt::Display`] impls use a separate compact form (`"input:N"` / `"pip:N"`, case-insensitive) for stored block properties.
    - object — A regular video input by index.
      - `input` integer, required — A regular video input by index.
    - object — A configured PiP composition by index.
      - `pip` integer, required — A configured PiP composition by index.

## Response `200`

Preview source selected

- SelectPreviewResponse — Response after selecting a preview source.
  - `message` string, required
  - `preview_input` integer, nullable — Current PVW input. `None` when PVW is a PiP source.
  - `preview_pip` integer, nullable — PiP index currently displayed on PVW, or `None` if PVW is an input.
  - `program_input` integer, nullable — Current PGM input. `None` when PGM is a PiP source.
  - `program_pip` integer, nullable — PiP index currently displayed on PGM, or `None` if PGM is an input.

## Other responses

- `400` — Invalid request
- `404` — Flow or block not found

## Changes

> 25 revisions in range; 17 could not be searched.

- **2026-04-07** `1e67862a080e` — 1 breaking
  - api removed without deprecation

[Change history](https://skmtc.dev/eyevinn/apis/strom-api/changes/api/flows/:flow_id/blocks/:block_id/preview/put.md)

---

[API](https://skmtc.dev/eyevinn/apis/strom-api.md) · [All operations](https://skmtc.dev/eyevinn/apis/strom-api/llms.txt) · [OpenAPI document](https://skmtc-service-production.skmtc.workers.dev/v1/apis/eyevinn/strom-api/revisions/0df7ca64263f/schema)