Extend Prefix
The client provides a convenient way to interact with the model API.
npm install --save @fal-ai/clientSet FAL_KEY as an environment variable in your runtime.
export FAL_KEY="YOUR_API_KEY"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("fal-ai/ltx23-trainer-v2/extend-prefix", {
input: {
training_data_url: ""
},
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);The API uses an API Key for authentication. It is recommended you set the FAL_KEY environment variable in your runtime when possible.
import { fal } from "@fal-ai/client";
fal.config({
credentials: "YOUR_FAL_KEY"
});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("fal-ai/ltx23-trainer-v2/extend-prefix", {
input: {
training_data_url: ""
},
webhookUrl: "https://optional.webhook.url/for/results",
});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("fal-ai/ltx23-trainer-v2/extend-prefix", {
requestId: "764cabcf-b745-4b3e-ae38-1200304cf45b",
logs: true,
});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("fal-ai/ltx23-trainer-v2/extend-prefix", {
requestId: "764cabcf-b745-4b3e-ae38-1200304cf45b"
});
console.log(result.data);
console.log(result.requestId);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.
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.
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.
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.
training_data_url string* requiredURL to a .zip archive of your training data. The exact file layout depends on the training mode — see this endpoint's documentation for the required structure. You can include a .txt caption alongside each media file (same base name).
rank RankEnumThe rank of the LoRA adaptation. Higher values increase capacity but use more memory. Default value: "32"
Possible enum values: 8, 16, 32, 64, 128
number_of_steps integerThe number of training steps. Default value: 2000
learning_rate floatLearning rate for optimization. Default value: 0.0002
number_of_frames integerNumber of frames per training sample. Must satisfy frames % 8 == 1 (e.g., 1, 9, 17, 25, 33, 41, 49, 57, 65, 73, 81, 89, 97). Default value: 89
frame_rate integerTarget frames per second for the training video (LTX-2.3 native is 24). Default value: 24
resolution ResolutionEnumResolution to use for training. Higher resolutions require more memory. Default value: "medium"
Possible enum values: low, medium, high
aspect_ratio AspectRatioEnumAspect ratio to use for training. Default value: "1:1"
Possible enum values: 16:9, 1:1, 9:16
trigger_phrase stringA phrase that will trigger the LoRA style. Will be prepended to captions during training. Default value: ""
auto_scale_input booleanIf true, videos will be automatically scaled to the target frame count and fps. This option has no effect on image datasets.
split_input_into_scenes booleanIf true, videos above a certain duration threshold will be split into scenes. Default value: true
split_input_duration_threshold floatThe duration threshold in seconds. If a video is longer than this, it will be split into scenes. Default value: 30
debug_dataset booleanWhen enabled, the trainer returns a downloadable archive of your preprocessed training data for manual inspection. Use this to verify that your videos, images, and captions were processed correctly before committing to a full training run.
with_audio booleanSet true to jointly extend audio AND video — the model continues both from the same prefix window. Requires every training clip AND each validation clip to contain an audio track. Default (false): video-only extension (silent output).
audio_normalize booleanPeak-normalize audio for consistent levels across the dataset. Default value: true
audio_preserve_pitch booleanPreserve pitch when fitting audio to video duration (vs trimming/padding). Default value: true
conditioning_frames integerNumber of leading PIXEL frames used as the clean prefix condition (for audio too, when with_audio). Must be ≡ 1 (mod 8) (e.g. 9, 17, 25). Converted to the latent temporal_boundary (conditioning_frames-1)//8+1, which must be smaller than the clip's latent length so there is a continuation to generate. Default value: 9
A list of validation prompts, each with a video to extend forward.
validation_negative_prompt stringA negative prompt to use for validation. Note: validation previews are single-stage approximations of the production two-stage (distilled) inference, so preview quality and guidance differ from final inference. Default value: "blurry, out of focus, overexposed, underexposed, low contrast, washed out colors, excessive noise, grainy texture, poor lighting, flickering, motion blur, distorted proportions, unnatural skin tones, deformed facial features, asymmetrical face, missing facial features, extra limbs, disfigured hands, wrong hand count, artifacts around text, inconsistent perspective, camera shake, incorrect depth of field, background too sharp, background clutter, distracting reflections, harsh shadows, inconsistent lighting direction, color banding, cartoonish rendering, 3D CGI look, unrealistic materials, uncanny valley effect, incorrect ethnicity, wrong gender, exaggerated expressions, wrong gaze direction, mismatched lip sync, silent or muted audio, distorted voice, robotic voice, echo, background noise, off-sync audio, incorrect dialogue, added dialogue, repetitive speech, jittery movement, awkward pauses, incorrect timing, unnatural transitions, inconsistent framing, tilted camera, flat lighting, inconsistent tone, cinematic oversaturation, stylized filters, or AI artifacts."
validation_number_of_frames integerThe number of frames in validation videos. Default value: 89
validation_frame_rate integerTarget frames per second for validation videos (LTX-2.3 native is 24). Default value: 24
validation_resolution ValidationResolutionEnumThe resolution to use for validation. Default value: "high"
Possible enum values: low, medium, high
validation_aspect_ratio ValidationAspectRatioEnumThe aspect ratio to use for validation. Default value: "1:1"
Possible enum values: 16:9, 1:1, 9:16
stg_scale floatSTG (Spatio-Temporal Guidance) scale. 0.0 disables STG. Recommended value is 1.0. Default value: 1
{
"training_data_url": "",
"rank": 32,
"number_of_steps": 2000,
"learning_rate": 0.0002,
"number_of_frames": 89,
"frame_rate": 24,
"resolution": "medium",
"aspect_ratio": "1:1",
"trigger_phrase": "",
"auto_scale_input": false,
"split_input_into_scenes": true,
"split_input_duration_threshold": 30,
"audio_normalize": true,
"audio_preserve_pitch": true,
"conditioning_frames": 9,
"validation": [],
"validation_negative_prompt": "blurry, out of focus, overexposed, underexposed, low contrast, washed out colors, excessive noise, grainy texture, poor lighting, flickering, motion blur, distorted proportions, unnatural skin tones, deformed facial features, asymmetrical face, missing facial features, extra limbs, disfigured hands, wrong hand count, artifacts around text, inconsistent perspective, camera shake, incorrect depth of field, background too sharp, background clutter, distracting reflections, harsh shadows, inconsistent lighting direction, color banding, cartoonish rendering, 3D CGI look, unrealistic materials, uncanny valley effect, incorrect ethnicity, wrong gender, exaggerated expressions, wrong gaze direction, mismatched lip sync, silent or muted audio, distorted voice, robotic voice, echo, background noise, off-sync audio, incorrect dialogue, added dialogue, repetitive speech, jittery movement, awkward pauses, incorrect timing, unnatural transitions, inconsistent framing, tilted camera, flat lighting, inconsistent tone, cinematic oversaturation, stylized filters, or AI artifacts.",
"validation_number_of_frames": 89,
"validation_frame_rate": 24,
"validation_resolution": "high",
"validation_aspect_ratio": "1:1",
"stg_scale": 1
}Combined validation video preview (video-producing endpoints), if any.
Combined validation audio preview for the audio-only-output endpoints (/v2a, /a2a, /t2a, /audio-extend-prefix, /audio-extend-suffix, /audio-inpaint), if any.
URL to the trained LoRA weights (.safetensors).
Configuration used for setting up inference endpoints.
Downloadable archive of the preprocessed training data, when debug_dataset is enabled.
{
"lora_file": {
"url": "",
"content_type": "image/png",
"file_name": "z9RV14K95DvU.png",
"file_size": 4404019
},
"config_file": {
"url": "",
"content_type": "image/png",
"file_name": "z9RV14K95DvU.png",
"file_size": 4404019
}
}url string* requiredThe URL where the file can be downloaded from.
content_type stringThe mime type of the file.
file_name stringThe name of the file. It will be auto-generated if not provided.
file_size integerThe size of the file in bytes.
prompt string* requiredThe prompt to use for validation.
video_url string* requiredURL to the video the model should temporally extend.