Add LTX-2.X IC LoRA and HDR Pipelines

[dg845]

What does this PR do?

This PR adds two new LTX-2.X pipelines: LTX2InContextPipeline, which supports in-context (IC) conditioning (used for example by some IC LoRAs) and LTX2HDRPipeline, which supports the newly released high dynamic range (HDR) pipeline (and HDR IC-LoRA) introduced in the LTX LumiVid paper.

This PR also updates LTX2ConditionPipeline to follow the LTX-2 repo's current image conditioning strategy, which overwrites the noisy latents only for first-frame (I2V) conditions and treats non-first-frame as keyframe conditions which are appended to the noisy latents. (Previously, the pipeline overwrote the noisy latents at all latent indices.)

Here is an example of using LTX2InContextPipeline with the Lightricks/LTX-2-19b-LoRA-Camera-Control-Dolly-In IC LoRA, which biases the generated video toward panning in on the subject:

LTX-2.3 IC LoRA Example Script

import torch

from diffusers import LTX2InContextPipeline
from diffusers.pipelines.ltx2.export_utils import encode_video
from diffusers.pipelines.ltx2.utils import DEFAULT_NEGATIVE_PROMPT


pipe = LTX2InContextPipeline.from_pretrained("dg845/LTX-2.3-Diffusers", torch_dtype=torch.bfloat16)
pipe.enable_model_cpu_offload(device="cuda:0")
pipe.load_lora_weights(
    "Lightricks/LTX-2-19b-LoRA-Camera-Control-Dolly-In",
    adapter_name="ic_lora",
    weight_name="ltx-2-19b-lora-camera-control-dolly-in.safetensors",
)
pipe.set_adapters("ic_lora", 1.0)

# If the IC LoRA uses reference conditions, you can specify them as follows:
# reference_video = load_video("reference.mp4")
# ref_cond = LTX2ReferenceCondition(frames=reference_video, strength=1.0)

prompt = "A flowing river in a forest"
frame_rate = 24.0
video, audio = pipe(
    prompt=prompt,
    negative_prompt=DEFAULT_NEGATIVE_PROMPT,
    # reference_conditions=[ref_cond],
    width=768,
    height=512,
    num_frames=121,
    frame_rate=frame_rate,
    num_inference_steps=30,
    guidance_scale=3.0,
    output_type="np",
    return_dict=False,
)

encode_video(
    video[0],
    fps=frame_rate,
    audio=audio[0].float().cpu(),
    audio_sample_rate=pipe.vocoder.config.output_sampling_rate,
    output_path="ltx2_ic_lora_output.mp4",
)

ltx2_ic_lora_output.mp4

And here is an example of using LTX2HDRPipeline with the Lightricks/LTX-2.3-22b-IC-LoRA-HDR HDR IC-LoRA, using the video above as the reference:

LTX-2.3 HDR IC LoRA Example Script

import torch
from safetensors import safe_open

from diffusers import LTX2HDRPipeline
from diffusers.pipelines.ltx2.export_utils import encode_hdr_tensor_to_mp4
from diffusers.pipelines.ltx2.pipeline_ltx2_hdr_lora import LTX2HDRReferenceCondition
from diffusers.pipelines.ltx2.utils import DISTILLED_SIGMA_VALUES
from diffusers.utils import load_video


pipe = LTX2HDRPipeline.from_pretrained("dg845/LTX-2.3-Distilled-Diffusers", torch_dtype=torch.bfloat16)
pipe.enable_model_cpu_offload(device="cuda")
pipe.load_lora_weights(
    "Lightricks/LTX-2.3-22b-IC-LoRA-HDR",
    adapter_name="hdr_lora",
    weight_name="ltx-2.3-22b-ic-lora-hdr-0.9.safetensors",
)
pipe.set_adapters("hdr_lora", 1.0)

reference_video = load_video("ltx2_ic_lora_output.mp4")
ref_cond = LTX2HDRReferenceCondition(frames=reference_video, strength=1.0)

# Load pre-computed HDR LoRA connector embeddings.
with safe_open(
    "/path/to/ltx-2.3-22b-ic-lora-hdr-scene-emb.safetensors", framework="pt", device="cuda"
) as f:
    connector_video_embeds = f.get_tensor("video_context")
    connector_audio_embeds = f.get_tensor("audio_context")

# `hdr_video` is a linear HDR tensor of shape (batch, frames, H, W, C).
hdr_video = pipe(
    reference_conditions=[ref_cond],
    connector_video_embeds=connector_video_embeds,
    connector_audio_embeds=connector_audio_embeds,
    width=768,
    height=512,
    num_frames=121,
    frame_rate=24.0,
    num_inference_steps=8,
    sigmas=DISTILLED_SIGMA_VALUES,
    guidance_scale=1.0,
    output_type="pt",
    return_dict=False,
)[0]

# Convert the HDR video to a SDR sRGB-tonemapped `.mp4` video.
# You can also save the output to EXR using `save_hdr_video_frames_as_exr`.
# A custom tone-mapper can be specified via the `tone_mapping_fn` argument.
encode_hdr_tensor_to_mp4(
    hdr_video[0],
    output_mp4="ltx2_hdr_lora_output.mp4",
    frame_rate=24.0,
)

ltx2_hdr_lora_output.mp4

This uses the default tone-mapper that simply clips HDR values to [0, 1], which is also used by the original LTX-2 code.

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members/contributors who may be interested in your PR.

@yiyixuxu
@sayakpaul
@linoytsaban

[HuggingFaceDocBuilderDev]

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[yiyixuxu]

I think with this PR, encode_hdr_tensor_to_mp4 is enough, no?
can we remove all the other functions here?

[yiyixuxu]

did they change the default since the release? 🤯

[dg845]

I ended up changing the LTX2ConditionPipeline.__call__ defaults to the LTX-2.3 defaults (since the implementation now follows the newest behavior rather than the original LTX-2.0 behavior); num_inference_steps=30 is the default for LTX-2.3, while num_inference_steps=40 is the default for LTX-2.0.