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blackforestlabs/flux-3/first-last-frame-to-video

FLUX.3 is Black Forest Labs' frontier video model. This endpoint generates the video between a defined start and end frame, interpolating a smooth, coherent transition from the first image to the last.
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Table of contents

About

Generate a video between a start frame and an end frame using FLUX 3.

Two bare keyframes pin the start and the end of the clip (the GA i2v contract).

1. Calling the API#

Install the client#

The client provides a convenient way to interact with the model API.

npm install --save @fal-ai/client

Setup your API Key#

Set FAL_KEY as an environment variable in your runtime.

export FAL_KEY="YOUR_API_KEY"

Submit a request#

The client API handles the API submit protocol. It will handle the request status updates and return the result when the request is completed.

import { fal } from "@fal-ai/client";

const result = await fal.subscribe("blackforestlabs/flux-3/first-last-frame-to-video", {
  input: {
    prompt: "A red panda walks along a mossy log in a sunlit forest, one continuous unbroken shot. Ambient birdsong and rustling leaves.",
    start_image_url: "https://storage.googleapis.com/falserverless/example_inputs/veo31-flf2v-input-1.jpeg",
    end_image_url: "https://storage.googleapis.com/falserverless/example_inputs/veo31-flf2v-input-2.jpeg"
  },
  logs: true,
  onQueueUpdate: (update) => {
    if (update.status === "IN_PROGRESS") {
      update.logs.map((log) => log.message).forEach(console.log);
    }
  },
});
console.log(result.data);
console.log(result.requestId);

2. Authentication#

The API uses an API Key for authentication. It is recommended you set the FAL_KEY environment variable in your runtime when possible.

API Key#

In case your app is running in an environment where you cannot set environment variables, you can set the API Key manually as a client configuration.
import { fal } from "@fal-ai/client";

fal.config({
  credentials: "YOUR_FAL_KEY"
});

3. Queue#

Submit a request#

The client API provides a convenient way to submit requests to the model.

import { fal } from "@fal-ai/client";

const { request_id } = await fal.queue.submit("blackforestlabs/flux-3/first-last-frame-to-video", {
  input: {
    prompt: "A red panda walks along a mossy log in a sunlit forest, one continuous unbroken shot. Ambient birdsong and rustling leaves.",
    start_image_url: "https://storage.googleapis.com/falserverless/example_inputs/veo31-flf2v-input-1.jpeg",
    end_image_url: "https://storage.googleapis.com/falserverless/example_inputs/veo31-flf2v-input-2.jpeg"
  },
  webhookUrl: "https://optional.webhook.url/for/results",
});

Fetch request status#

You can fetch the status of a request to check if it is completed or still in progress.

import { fal } from "@fal-ai/client";

const status = await fal.queue.status("blackforestlabs/flux-3/first-last-frame-to-video", {
  requestId: "764cabcf-b745-4b3e-ae38-1200304cf45b",
  logs: true,
});

Get the result#

Once the request is completed, you can fetch the result. See the Output Schema for the expected result format.

import { fal } from "@fal-ai/client";

const result = await fal.queue.result("blackforestlabs/flux-3/first-last-frame-to-video", {
  requestId: "764cabcf-b745-4b3e-ae38-1200304cf45b"
});
console.log(result.data);
console.log(result.requestId);

4. Files#

Some attributes in the API accept file URLs as input. Whenever that's the case you can pass your own URL or a Base64 data URI.

Data URI (base64)#

You can pass a Base64 data URI as a file input. The API will handle the file decoding for you. Keep in mind that for large files, this alternative although convenient can impact the request performance.

Hosted files (URL)#

You can also pass your own URLs as long as they are publicly accessible. Be aware that some hosts might block cross-site requests, rate-limit, or consider the request as a bot.

Uploading files#

We provide a convenient file storage that allows you to upload files and use them in your requests. You can upload files using the client API and use the returned URL in your requests.

import { fal } from "@fal-ai/client";

const file = new File(["Hello, World!"], "hello.txt", { type: "text/plain" });
const url = await fal.storage.upload(file);

Read more about file handling in our file upload guide.

5. Schema#

Input#

prompt string* required

The text prompt describing the video you want to generate.

aspect_ratio AspectRatioEnum

Aspect ratio of the generated video. auto lets the model choose. Default value: "auto"

Possible enum values: auto, 21:9, 2:1, 16:9, 4:3, 1:1, 3:4, 9:16

resolution ResolutionEnum

Resolution of the generated video. Default value: "720p"

Possible enum values: 720p, 1080p

duration DurationEnum

Duration of the generated video in seconds. An explicit duration is required to place the end frame. Default value: "5"

Possible enum values: 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20

generate_audio boolean

Whether to generate audio for the video. Default value: true

safety_tolerance integer

The safety tolerance level for the generated video. 0 is the strictest and 4 is the most permissive. Default value: 2

start_image_url string* required

URL of the image used as the first frame of the video (PNG, JPEG, or WebP).

end_image_url string* required

URL of the image used as the last frame of the video (PNG, JPEG, or WebP).

{
  "prompt": "A red panda walks along a mossy log in a sunlit forest, one continuous unbroken shot. Ambient birdsong and rustling leaves.",
  "aspect_ratio": "auto",
  "resolution": "720p",
  "duration": 5,
  "generate_audio": true,
  "safety_tolerance": 2,
  "start_image_url": "https://storage.googleapis.com/falserverless/example_inputs/veo31-flf2v-input-1.jpeg",
  "end_image_url": "https://storage.googleapis.com/falserverless/example_inputs/veo31-flf2v-input-2.jpeg"
}

Output#

video File* required

The generated video.

seed integer* required

The seed used for the generation.

{
  "video": {
    "url": "https://storage.googleapis.com/falserverless/example_outputs/veo3-i2v-output.mp4"
  }
}

Other types#

Flux3Keyframe#

image_url string* required

URL of the keyframe image (PNG, JPEG, or WebP).

frame_index integer* required

Frame position of this keyframe in the generated 24 fps video. Must be unique and at most duration * 24.

File#

url string* required

The URL where the file can be downloaded from.

content_type string

The mime type of the file.

file_name string

The name of the file. It will be auto-generated if not provided.

file_size integer

The size of the file in bytes.

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