packages/ltx-trainer/AGENTS.md

AGENTS.md

This file provides guidance to AI coding assistants (Claude, Cursor, etc.) when working with code in this repository.

Project Overview

LTX Trainer is a training toolkit for fine-tuning the Lightricks LTX audio-video generation models. It supports:

• Text-to-video (T2V) - Generate video from text prompts
• Text-to-audio (T2A) - Generate audio from text prompts
• Image-to-video (I2V) - Generate video conditioned on a first frame
• Video extension - Forward (prefix) and backward (suffix) video continuation
• Video inpainting - Mask-based spatial/temporal inpainting
• Video outpainting - Spatial crop-based outpainting
• IC-LoRA video-to-video - In-context control adapters for style/structure transfer
• Audio-to-video (A2V) and Video-to-audio (V2A) - Cross-modal generation with frozen conditioning
• Audio extension - Forward (prefix) and backward (suffix) audio continuation
• Audio inpainting - Mask-based audio inpainting
• IC-LoRA audio-to-audio (A2A) - Audio reference conditioning for style transfer
• AV2AV IC-LoRA - Combined video and audio reference conditioning
• LoRA training - Efficient fine-tuning with adapters
• Full fine-tuning - Complete model training

All conditioning scenarios are expressed through the unified FlexibleStrategy configuration.

Supported model versions:

• LTX-2 (19B, initial audio-video model)
• LTX-2.3 (22B, improved text conditioning and audio quality)

Version detection is fully automatic — ltx-core reads the checkpoint config and selects the correct architecture components. The trainer does not need version-specific code paths.

Key Dependencies:

• ltx-core - Core model implementations (transformer, VAE, text encoder, scheduler)
• ltx-pipelines - Inference pipeline components

Important: This trainer only supports LTX-2 and later (audio-video models). The older LTXV (video-only) models are not supported.

Architecture Overview

Package Structure

packages/ltx-trainer/
├── src/ltx_trainer/              # Main training module
│   ├── __init__.py               # Logger setup, path config
│   ├── config.py                 # Pydantic configuration models
│   ├── config_display.py         # Config pretty-printing
│   ├── trainer.py                # Main training orchestration with Accelerate
│   ├── model_loader.py           # Model loading using ltx-core
│   ├── validation_runner.py      # ValidationRunner — conditioned validation sampling
│   ├── datasets.py               # PrecomputedDataset, DummyDataset
│   ├── training_strategies/      # Strategy pattern for different training modes
│   │   ├── __init__.py           # Factory function: get_training_strategy()
│   │   ├── base_strategy.py      # TrainingStrategy ABC, ModelInputs, TrainingStrategyConfigBase
│   │   ├── flexible.py           # FlexibleStrategy, FlexibleStrategyConfig [RECOMMENDED]
│   │   ├── text_to_video.py      # TextToVideoStrategy, TextToVideoConfig [DEPRECATED]
│   │   └── video_to_video.py     # VideoToVideoStrategy, VideoToVideoConfig [DEPRECATED]
│   ├── timestep_samplers.py      # Flow matching timestep sampling
│   ├── gemma_8bit.py             # 8-bit Gemma text encoder loading (bitsandbytes)
│   ├── quantization.py           # Transformer INT8/INT4/FP8 quantization
│   ├── captioning.py             # Video captioning utilities
│   ├── video_utils.py            # Video I/O and processing
│   ├── gpu_utils.py              # GPU memory helpers
│   ├── hf_hub_utils.py           # HuggingFace Hub integration
│   ├── progress.py               # Training progress display
│   └── utils.py                  # Image I/O helpers
├── scripts/                      # User-facing CLI tools
│   ├── train.py                  # Main training script
│   ├── process_dataset.py        # Dataset preprocessing (latents + captions)
│   ├── process_videos.py         # Video latent encoding
│   ├── process_captions.py       # Text embedding computation
│   ├── caption_videos.py         # Automatic video captioning
│   ├── decode_latents.py         # Latent decoding for debugging
│   ├── compute_reference.py      # Generate IC-LoRA reference videos
│   └── split_scenes.py           # Scene detection and splitting
├── configs/                      # Example training configurations
│   ├── t2v_lora.yaml             # Text-to-video LoRA
│   ├── t2v_lora_low_vram.yaml    # Text-to-video LoRA (low VRAM)
│   ├── i2v_lora.yaml             # Image-to-video LoRA
│   ├── v2v_ic_lora.yaml          # IC-LoRA video-to-video
│   ├── a2v_lora.yaml             # Audio-to-video LoRA
│   ├── v2a_lora.yaml             # Video-to-audio LoRA
│   ├── video_extend_lora.yaml    # Video extension (forward)
│   ├── video_suffix_lora.yaml    # Video extension (backward)
│   ├── video_inpainting_lora.yaml # Video inpainting
│   ├── video_outpainting_lora.yaml # Video outpainting
│   ├── t2a_lora.yaml             # Text-to-audio LoRA
│   ├── audio_extend_lora.yaml    # Audio extension (forward)
│   ├── audio_suffix_lora.yaml    # Audio extension (backward)
│   ├── audio_inpainting_lora.yaml # Audio inpainting
│   ├── a2a_ic_lora.yaml          # Audio-to-audio IC-LoRA
│   ├── av2av_ic_lora.yaml        # AV2AV IC-LoRA
│   └── accelerate/               # FSDP, DDP configs
├── tests/                        # Pytest tests
└── docs/                         # Documentation

Key Architectural Patterns

Model Loading:

• ltx_trainer.model_loader provides component loaders using ltx-core
• Individual loaders: load_transformer(), load_video_vae_encoder(), load_video_vae_decoder(), load_text_encoder(), load_embeddings_processor(), etc.
• Combined loader: load_model() returns LtxModelComponents dataclass
• Uses SingleGPUModelBuilder from ltx-core internally
• Text encoder and embeddings processor are loaded separately (the text encoder only needs Gemma weights; the embeddings processor only needs the LTX checkpoint)
• 8-bit text encoder loading via gemma_8bit.py (bitsandbytes)

Training Flow:

1. Configuration loaded via Pydantic models in config.py
2. LtxvTrainer class orchestrates the training loop
3. Text encoder loaded on GPU → validation embeddings cached → heavy components unloaded (only embeddings_processor kept)
4. Each training step: embedding connectors applied → strategy prepares ModelInputs → transformer forward pass → strategy computes loss
5. Training strategies (FlexibleStrategy) handle mode-specific logic including conditioning, masking, and loss computation
6. Accelerate handles distributed training, mixed precision, and device placement
7. Data flows as precomputed latents through PrecomputedDataset

Model Interface (Modality-based):

from ltx_core.model.transformer.modality import Modality

video = Modality(
    enabled=True,
    latent=video_latents,  # [B, seq_len, 128] patchified latent tokens
    sigma=sigma,  # [B,] current noise level (per-batch)
    timesteps=video_timesteps,  # [B, seq_len] per-token timestep embeddings
    positions=video_positions,  # [B, 3, seq_len, 2] positional coordinates
    context=video_embeds,  # text conditioning embeddings
    context_mask=None,  # optional attention mask for text context
)
audio = Modality(
    enabled=True,
    latent=audio_latents,
    sigma=sigma,
    timesteps=audio_timesteps,
    positions=audio_positions,  # [B, 1, seq_len, 2]
    context=audio_embeds,
    context_mask=None,
)

# Forward pass returns predictions for both modalities
video_pred, audio_pred = model(video=video, audio=audio, perturbations=None)

Note: Modality is immutable (frozen dataclass). Use dataclasses.replace() to modify.

sigma vs timesteps: These serve different roles. timesteps is per-token (e.g. sigma * denoise_mask — conditioning tokens get 0, noisy tokens get sigma). sigma is per-batch and is used for prompt AdaLN conditioning ( LTX-2.3) and cross-modality (video↔audio) attention conditioning (both versions).

Configuration System:

• All config in src/ltx_trainer/config.py
• Main class: LtxTrainerConfig
• TrainingStrategyConfig - Union of FlexibleStrategyConfig | TextToVideoConfig (deprecated) | VideoToVideoConfig (deprecated)
• FlexibleStrategyConfig - Unified strategy config with video/audio ModalityConfig blocks
• ModalityConfig - Per-modality config: is_generated, latents_dir, conditions list
• ConditionConfig - Discriminated union: FirstFrameConditionConfig, PrefixConditionConfig, SuffixConditionConfig, SpatialCropConditionConfig, MaskConditionConfig, ReferenceConditionConfig
• ValidationSample - Per-sample validation config with prompt, conditions, optional video_dims/seed overrides
• ValidationCondition - Discriminated union for validation conditions (first_frame, prefix, suffix, spatial_crop, mask, reference, video_to_audio, audio_to_video)
• Uses Pydantic field validators and model validators
• Config uses extra="forbid" — unknown fields cause validation errors
• Config files in configs/ directory

LTX-2 vs LTX-2.3: Differences

Both model versions share the same latent space interface (see Latent Space Constants). The differences lie in how text conditioning and audio generation work. Version detection is automatic via checkpoint config — the trainer uses a unified API.

Component	LTX-2 (19B)	LTX-2.3 (22B)
Feature extractor	FeatureExtractorV1: single aggregate_embed, same output for video and audio	FeatureExtractorV2: separate video_aggregate_embed + audio_aggregate_embed, per-token RMSNorm
Caption projection	Inside the transformer (caption_projection)	Inside the feature extractor (before connector)
Embeddings connectors	Same dimensions for video and audio	Separate dimensions (AudioEmbeddings1DConnectorConfigurator)
Prompt AdaLN	Not present (cross_attention_adaln=False)	Active — modulates cross-attention to text using sigma
Vocoder	HiFi-GAN (Vocoder)	BigVGAN v2 + bandwidth extension (VocoderWithBWE)

How version detection works in ltx-core:

• Feature extractor: _create_feature_extractor() checks for V2 config keys (caption_proj_before_connector, etc.). Present → V2; absent → V1.
• Vocoder: VocoderConfigurator checks for config["vocoder"]["bwe"]. Present → VocoderWithBWE; absent → Vocoder.
• Transformer: _build_caption_projections() checks caption_proj_before_connector. True (V2) → no caption projection in transformer; False (V1) → caption projection created in transformer.
• Embeddings connectors: AudioEmbeddings1DConnectorConfigurator reads audio_connector_* keys, falling back to video connector keys for V1 backward compatibility.

Text Encoder Pipeline

The GemmaTextEncoder implements a 3-block pipeline:

1. Block 1 — Gemma LLM: Tokenizes text → runs through Gemma → extracts hidden states
2. Block 2 — Feature extractor: Hidden states → normalized features (V1: single stream duplicated for video/audio; V2: separate video and audio projections)
3. Block 3 — Embeddings processor: Features → embeddings connectors → final context embeddings for the transformer

Precomputed embeddings (offline): process_captions.py runs Blocks 1+2 via text_encoder.precompute() and saves the results. Block 3 (connectors) is applied during training via text_encoder.embeddings_processor.create_embeddings().

Precomputed embeddings formats:

• New format (from precompute()): saves video_prompt_embeds, audio_prompt_embeds (optional), prompt_attention_mask
• Legacy format (from old _preprocess_text()): saves prompt_embeds, prompt_attention_mask

The trainer handles both formats in _training_step(): if video_prompt_embeds is present, it uses the new format; otherwise, it duplicates prompt_embeds for both modalities (mirroring V1 behavior).

After caching validation embeddings, the trainer unloads heavy components to free VRAM:

self._text_encoder.model = None
self._text_encoder.tokenizer = None
self._text_encoder.feature_extractor = None
# Only embeddings_processor (connectors) remains — used during training

Latent Space Constants

These values are shared across all supported model versions:

Constant	Value	Where used
Video latent channels	128	VAE encoder/decoder, patchifier, VideoLatentShape
Spatial compression	32× (H and W)	SpatioTemporalScaleFactors.default(), config validators
Temporal compression	8×	SpatioTemporalScaleFactors.default(), config validators
Frame constraint	frames % 8 == 1	Config validators, validation runner
Resolution constraint	Width and height divisible by 32	Config validators, validation runner
Audio latent channels	8	AudioLatentShape, audio patchifier
Audio mel bins	16	AudioLatentShape, audio patchifier
Patchified token dim (video)	128 (128 × 1 × 1 × 1)	Transformer in_channels
Patchified token dim (audio)	128 (8 × 16)	Transformer audio_in_channels

Development Commands

Setup and Installation

# From the repository root
uv sync
cd packages/ltx-trainer

Code Quality

# Run ruff linting and formatting
uv run ruff check .
uv run ruff format .

# Run pre-commit checks
uv run pre-commit run --all-files

Running Tests

cd packages/ltx-trainer
uv run pytest

Running Training

# Single GPU
uv run python scripts/train.py configs/t2v_lora.yaml

# Multi-GPU with Accelerate
uv run accelerate launch scripts/train.py configs/t2v_lora.yaml

Testing Standards

Structure

• Flat functions only — use def test_*(), never class Test* with methods. Pytest collects standalone functions.
• Only test public interfaces — never call private methods (_method) directly. Verify private behavior indirectly through the public API.

What to Test

• Custom validators and business logic — cross-field validators, domain constraints, error paths. These catch real bugs.
• Behavioral tests — call the public method, verify the outputs have the right shape, values, and structure. One behavioral test is worth ten config-only tests.
• Edge cases and error paths — boundary conditions, composed behaviors, expected exceptions.
• Contract tests — required fields, rejected invalid inputs, safety mechanisms like extra="forbid".

What NOT to Test

• Pydantic storing a value — Foo(x=1); assert foo.x == 1 tests Pydantic, not your code. If a behavioral test already creates the same config and uses it, the config-only test adds nothing.
• Pydantic Literal defaults — assert config.type == "first_frame" when type is Literal["first_frame"].
• Pydantic default factories — assert config.conditions == [] when the field has default_factory=list.
• Tests already covered by behavioral tests — if test_prefix_conditioning creates a valid PrefixConditionConfig and exercises it end-to-end, a separate test_prefix_valid that just creates the same config is redundant.
• Trivial instantiation tests — strategy = Strategy(config); assert strategy.config is not None when every other test creates a strategy.

Keeping Tests DRY

• Use helper functions for repeated setup patterns (e.g., _make_strategy(video=_video_modality(...)) instead of 6-8 lines of config/strategy creation per test).
• Use named constants for test dimensions (e.g., VIDEO_SEQ_LEN, TOKENS_PER_FRAME) instead of magic numbers.
• Merge tests that share identical setup — when 5+ tests call prepare_training_inputs with the exact same config and batch, each checking one assertion, merge them into one test that checks all assertions. Pytest reports the exact failing line anyway.
• Use @pytest.mark.parametrize for the same logic tested with different inputs (e.g., valid/invalid values for a field).
• Use pytest fixtures for shared batch data and test directories, but prefer explicit helper functions over fixtures for strategy/config creation (makes the test self-documenting).

Code Standards

Type Hints

• Always use type hints for all function arguments and return values
• Use Python 3.10+ syntax: list[str] not List[str], str | Path not Union[str, Path]
• Use pathlib.Path for file operations

Class Methods

• Mark methods as @staticmethod if they don't access instance or class state
• Use @classmethod for alternative constructors

AI/ML Specific

• Use @torch.inference_mode() for inference (prefer over @torch.no_grad())
• Use accelerator.device for distributed compatibility
• Support mixed precision (bfloat16 via dtype parameters)
• Use gradient checkpointing for memory-intensive training

Logging

• Use from ltx_trainer import logger for all messages
• Avoid print statements in production code

Important Files & Modules

Configuration (CRITICAL)

src/ltx_trainer/config.py - Master config definitions

Key classes:

• LtxTrainerConfig - Main configuration container
• ModelConfig - Model paths, training mode (lora | full), checkpoint loading
• TrainingStrategyConfig - Union of FlexibleStrategyConfig | TextToVideoConfig (deprecated) | VideoToVideoConfig (deprecated)
• FlexibleStrategyConfig - Unified strategy config with video/audio ModalityConfig blocks
• ModalityConfig - Per-modality config: is_generated, latents_dir, conditions list
• ConditionConfig - Discriminated union: FirstFrameConditionConfig, PrefixConditionConfig, SuffixConditionConfig, SpatialCropConditionConfig, MaskConditionConfig, ReferenceConditionConfig
• ValidationSample - Per-sample validation config with prompt, conditions, optional video_dims/seed overrides
• ValidationCondition - Discriminated union for validation conditions (first_frame, prefix, suffix, spatial_crop, mask, reference, video_to_audio, audio_to_video)
• LoraConfig - Rank, alpha, dropout, target modules
• OptimizationConfig - Learning rate, batch size, gradient accumulation, scheduler, gradient checkpointing
• AccelerationConfig - Mixed precision, quantization, 8-bit text encoder
• DataConfig - Preprocessed data root, dataloader workers
• ValidationConfig - Prompts, video dimensions, CFG/STG guidance, audio generation, inference steps
• CheckpointsConfig - Save interval, retention, precision
• FlowMatchingConfig - Timestep sampling mode and parameters
• HubConfig - HuggingFace Hub push settings
• WandbConfig - Weights & Biases logging

⚠️ When modifying config.py:

1. Update ALL config files in configs/
2. Update docs/configuration-reference.md
3. Test that all configs remain valid

Training Core

src/ltx_trainer/trainer.py - Main training loop (LtxvTrainer)

• Implements distributed training with Accelerate
• Handles mixed precision, gradient accumulation, checkpointing
• _training_step() applies embedding connectors then delegates to strategy
• _load_text_encoder_and_cache_embeddings() loads the text encoder + embeddings processor, caches validation embeddings, then unloads the Gemma LLM (keeps only the embeddings processor connectors for training)
• Uses training strategies for mode-specific logic

src/ltx_trainer/training_strategies/ - Strategy pattern

• base_strategy.py: TrainingStrategy ABC, ModelInputs dataclass
• flexible.py: FlexibleStrategy — unified conditioning framework (recommended)
• text_to_video.py: TextToVideoStrategy (deprecated — use FlexibleStrategy)
• video_to_video.py: VideoToVideoStrategy (deprecated — use FlexibleStrategy)

Key methods each strategy implements:

• prepare_training_inputs() - Convert batch to ModelInputs with Modality objects
• compute_loss() - Calculate training loss (velocity prediction, MSE with masking)

The strategy's config declares its data directories via get_data_sources() (single source of truth, used for both dataset wiring and existence validation).

src/ltx_trainer/model_loader.py - Model loading

Component loaders:

• load_transformer() → LTXModel
• load_video_vae_encoder() → VideoEncoder
• load_video_vae_decoder() → VideoDecoder
• load_audio_vae_decoder() → AudioDecoder
• load_vocoder() → Vocoder or VocoderWithBWE (auto-detected)
• load_text_encoder(gemma_model_path) → GemmaTextEncoder (pure Gemma LLM, no checkpoint needed)
• load_embeddings_processor(checkpoint_path) → EmbeddingsProcessor (feature extractor + connectors)
• load_model() → LtxModelComponents (convenience wrapper)

src/ltx_trainer/validation_runner.py - Conditioned validation sampling

• Manages the full validation lifecycle: embedding caching, media encoding, denoising, decoding
• Supports all validation condition types: first_frame, prefix, suffix, spatial_crop, mask, reference, video_to_audio, audio_to_video
• Handles frozen modality paths (sigma=0 for conditioning modality)
• Builds conditioning items using ltx-core's VideoConditionByLatentIndex, VideoConditionByReferenceLatent, VideoConditionByMask
• Optional side-by-side reference output for IC-LoRA validation

src/ltx_trainer/timestep_samplers.py - Flow matching timestep sampling

• UniformTimestepSampler - Uniform sampling in [min, max]
• ShiftedLogitNormalTimestepSampler - Stretched shifted logit-normal distribution with:
  • Shift determined by sequence length (more noise at higher token counts)
  • Percentile stretching for better [0, 1] coverage
  • Uniform fallback (10% of samples) to prevent distribution collapse
  • Reflection around eps for numerical stability near zero

src/ltx_trainer/gemma_8bit.py - 8-bit text encoder loading

Bypasses ltx-core's standard loading path to enable bitsandbytes 8-bit quantization of the Gemma backbone. Manually constructs the GemmaTextEncoder with quantized model, feature extractor, and embeddings processor.

Data

src/ltx_trainer/datasets.py - Dataset handling

• PrecomputedDataset loads pre-computed VAE latents and text embeddings
• Supports video latents, audio latents, text embeddings, reference video latents, reference audio latents, video masks, and audio masks
• Handles legacy patchified format [seq_len, C] → automatically unpatchifies to [C, F, H, W]
• DummyDataset for benchmarking and minimal testing

Common Development Tasks

Agent-Assisted Training

When a user asks to train, fine-tune, create a LoRA, or produce a custom LTX-2 model, use the repository skill at .claude/skills/train-model. The skill is the orchestrator for dataset probing, mode selection, preprocessing, training launch, monitoring, and post-train validation; it treats packages/ltx-trainer/docs/ as the source of truth.

Adding a New Configuration Parameter

1. Add field to appropriate config class in src/ltx_trainer/config.py
2. Add validator if needed
3. Update ALL config files in configs/
4. Update docs/configuration-reference.md

Implementing a New Training Strategy

The FlexibleStrategy now covers all use cases (T2V, T2A, I2V, V2V, A2A, AV2AV, inpainting, outpainting, extension, A2V, V2A, IC-LoRA) through configuration alone. A new strategy is only needed for fundamentally different training paradigms that cannot be expressed via ModalityConfig + ConditionConfig combinations.

If you do need a new strategy:

1. Create new file in src/ltx_trainer/training_strategies/
2. Create config class inheriting TrainingStrategyConfigBase and implement get_data_sources()
3. Create strategy class inheriting TrainingStrategy
4. Implement: prepare_training_inputs(), compute_loss()
5. Add to __init__.py: import, add to TrainingStrategyConfig union, update factory
6. Add discriminator tag to config.py's TrainingStrategyConfig
7. Create example config file in configs/

Working with Modalities

from dataclasses import replace
from ltx_core.model.transformer.modality import Modality

# Create modality — all fields except enabled and masks are required
video = Modality(
    enabled=True,
    latent=latents,  # [B, seq_len, 128]
    sigma=sigma,  # [B,] — the per-batch noise level
    timesteps=timesteps,  # [B, seq_len] — per-token (sigma * denoise_mask)
    positions=positions,  # [B, 3, seq_len, 2]
    context=context,  # text embeddings from embeddings_processor
    context_mask=None,
)

# Update (immutable — must use replace)
video = replace(video, latent=new_latent, sigma=new_sigma, timesteps=new_timesteps)

# Disable a modality
audio = replace(audio, enabled=False)

Working with the Text Encoder

# Full forward pass (used for validation — runs all 3 blocks)
video_embeds, audio_embeds, attention_mask = text_encoder(prompt)

# Precompute features (used in process_captions.py — runs blocks 1+2 only)
video_features, audio_features, attention_mask = text_encoder.precompute(prompt, padding_side="left")

# Apply connectors during training (block 3 only)
additive_mask = text_encoder._convert_to_additive_mask(attention_mask, video_features.dtype)
video_embeds, audio_embeds, binary_mask = text_encoder.embeddings_processor.create_embeddings(
    video_features, audio_features, additive_mask
)

Debugging Tips

Training Issues:

• Check logs first (rich logger provides context)
• GPU memory: Look for OOM errors, enable enable_gradient_checkpointing: true
• Distributed training: Check accelerator.state and device placement

Model Loading:

• Ensure model_path points to a local .safetensors file
• Ensure text_encoder_path points to a Gemma model directory
• URLs are NOT supported for model paths
• For 8-bit loading: ensure bitsandbytes is installed

Configuration:

• Validation errors: Check validators in config.py
• Unknown fields: Config uses extra="forbid" — all fields must be defined
• FlexibleStrategy requires at least one modality with is_generated: true
• Audio modality cannot use first_frame or spatial_crop conditions

Precomputed Data:

• Legacy data (prompt_embeds) works via backward-compat in _training_step()
• New data (video_prompt_embeds + audio_prompt_embeds) is the expected format
• Latents must be in [C, F, H, W] format (legacy [seq_len, C] is auto-converted)

Key Constraints

Frame Requirements

Frames must satisfy frames % 8 == 1:

• ✅ Valid: 1, 9, 17, 25, 33, 41, 49, 57, 65, 73, 81, 89, 97, 121
• ❌ Invalid: 24, 32, 48, 64, 100

Resolution Requirements

Width and height must be divisible by 32.

Model Paths

• Must be local paths (URLs not supported)
• model_path: Path to .safetensors checkpoint
• text_encoder_path: Path to Gemma model directory

Platform Requirements

• Linux required (uses triton which is Linux-only)
• CUDA GPU with 32GB+ VRAM recommended

Reference: ltx-core Key Components

packages/ltx-core/src/ltx_core/
├── model/
│   ├── transformer/
│   │   ├── model.py                # LTXModel (diffusion transformer)
│   │   ├── modality.py             # Modality dataclass
│   │   ├── transformer.py          # BasicAVTransformerBlock
│   │   ├── transformer_args.py     # TransformerArgsPreprocessor (sigma → prompt AdaLN)
│   │   ├── model_configurator.py   # LTXModelConfigurator (version-aware)
│   │   └── timestep_embedding.py   # Timestep/sigma embedding
│   ├── video_vae/
│   │   ├── video_vae.py            # VideoEncoder, VideoDecoder
│   │   └── model_configurator.py   # VideoEncoderConfigurator, VideoDecoderConfigurator
│   ├── audio_vae/
│   │   ├── audio_vae.py            # AudioEncoder, AudioDecoder
│   │   └── vocoder.py              # Vocoder, VocoderWithBWE (output_sampling_rate)
│   └── common/                     # Shared model components
├── text_encoders/gemma/
│   ├── __init__.py                 # Exports: GemmaTextEncoder, GemmaTextEncoderConfigurator,
│   │                               #   AV_GEMMA_TEXT_ENCODER_KEY_OPS, GEMMA_MODEL_OPS,
│   │                               #   module_ops_from_gemma_root
│   ├── encoders/
│   │   ├── base_encoder.py         # GemmaTextEncoder (unified 3-block pipeline)
│   │   └── encoder_configurator.py # GemmaTextEncoderConfigurator, _create_feature_extractor
│   ├── feature_extractor.py        # FeatureExtractorV1 (19B), FeatureExtractorV2 (22B)
│   ├── embeddings_connector.py     # Embeddings1DConnector, Embeddings1DConnectorConfigurator,
│   │                               #   AudioEmbeddings1DConnectorConfigurator
│   ├── embeddings_processor.py     # EmbeddingsProcessor (wraps video + audio connectors)
│   └── tokenizer.py               # LTXVGemmaTokenizer
├── components/
│   ├── schedulers.py               # LTX2Scheduler
│   ├── diffusion_steps.py          # EulerDiffusionStep
│   ├── guiders.py                  # CFGGuider, STGGuider
│   └── patchifiers.py              # VideoLatentPatchifier, AudioPatchifier
├── conditioning/                   # ConditioningItem, mask_utils, types
├── tools.py                        # VideoLatentTools, AudioLatentTools
├── loader/
│   ├── single_gpu_model_builder.py # SingleGPUModelBuilder
│   ├── sft_loader.py              # SafetensorsModelStateDictLoader
│   └── sd_ops.py                  # Key remapping (SDOps)
└── types.py                       # SpatioTemporalScaleFactors, VideoLatentShape, AudioLatentShape