diffusers

7564fb01 - Ltx 2.5 (#14447)

Ltx 2.5 (#14447) * Add LTX-2.4 support to the LTX2 transformer, pipelines, and conversion script LTX-2.4 reuses the existing LTX2 model and pipeline classes. The delta over 2.3 is a small set of additive config flags plus a Gemma 3 -> Gemma 4 text encoder swap, so no new model or pipeline classes are introduced. - transformer_ltx2.py: add `ff_bias`/`audio_ff_bias` (2.4's video FFN drops its bias) and `use_prompt_adaln_single` (toggles timestep-dependent prompt cross-attention modulation; when off, cross-attention K/V becomes timestep-independent and cacheable across denoising steps for a given prompt). Both default to their 2.3 behavior. The flag is read back from `self.config` rather than mirrored onto an instance attribute, and all three new constructor args are documented. - pipeline_ltx2.py / pipeline_ltx2_image2video.py: add an optional `prompt_enhancer` component to both pipelines (previously T2V-only). LTX-2.4's fine-tuned text encoder is conditioning-only, so enhancement uses a separate off-the-shelf google/gemma-4-E2B-it checkpoint with its own message format and decoding recipe -- unlike LTX-2.0/2.3, where one checkpoint serves both roles. `enhance_prompt()` resolves the format and `.generate` kwargs from whichever model is active, and frees a dedicated enhancer from GPU memory right after use (guarded so it does not interfere with accelerate's offload hooks), mirroring the existing text_encoder handling. Both `__call__`s gain `enable_prompt_enhancement: bool | None = None`, which resolves to `True` when a dedicated `prompt_enhancer` is configured (LTX-2.4) or when `system_prompt` was passed explicitly (matching prior LTX-2.0/2.3 behavior exactly), and `False` otherwise. Explicit `False` disables enhancement even on 2.4. When enabled with no `system_prompt` on a 2.4 pipeline, the matching default system prompt is injected. `max_new_tokens`/`seed` keep their literal defaults (512/10) unconditionally: greedy decoding consumes no randomness, so `seed` is inert for the dedicated-enhancer case, and 512 tokens comfortably covers the target caption length. No public API or default changes were needed for LTX-2.0/2.3. Validation of the enhancement arguments happens in `check_inputs`, so an unsatisfiable request fails before the prompt is encoded rather than partway through generation. Text encoder, tokenizer, processor and enhancer type hints name the concrete Gemma classes they accept. - utils.py: add a `PromptEnhancementConfig` dataclass plus `GEMMA3_PROMPT_ENHANCEMENT_CONFIG`/`GEMMA4_PROMPT_ENHANCEMENT_CONFIG` as the single source of truth for each model's message prefix and `.generate` kwargs, shared by both pipelines. Add the validated "capstyle_plus" LTX2_4_T2V/I2V_DEFAULT_SYSTEM_PROMPT strings, marked `docstyle-ignore` so `doc-builder style` cannot re-wrap them -- the prompts must stay byte-for-byte identical to the reference, newlines included. - convert_ltx2_to_diffusers.py: add a "2.4" branch to all five get_ltx2_*_config functions. Transformer/VAE/vocoder configs are structurally identical to 2.3 (verified against the checkpoint's own safetensors metadata); only `ff_bias=False` differs. Connector `caption_channels`/`text_proj_in_factor` are now derived from the live Gemma text config rather than hardcoded, since 2.4's text encoder is not pinned to a single checkpoint the way Gemma-3-12B is for 2.0/2.3. Swap `Gemma3ForConditionalGeneration`/`Gemma3Processor` for `AutoModelForImageTextToText`/`AutoProcessor` so one path covers Gemma 3 and Gemma 4. Raise a clear error when --version 2.4 is requested without pointing --text_encoder_model_id at a Gemma 4 (gemma4_unified) checkpoint, and add --prompt_enhancer_model_id, required whenever --version 2.4 is combined with --add_processor, since falling back to --text_encoder_model_id (correct for 2.0/2.3) would pair 2.4 with the wrong enhancement model. Also fixes a pre-existing vocoder class-selection bug that only checked for "2.3", and `processor` never being passed into the --full_pipeline LTX2Pipeline(...) construction. - docs/source/en/api/pipelines/ltx2.md: add an "LTX-2.4" section covering what carries over from 2.3 unchanged (guidance recommendations, aside from a different STG block index) and what does not (a single-stage checkpoint only, with no two-stage or distilled workflow yet), plus the corrected prompt-enhancement recipe and its enabled-by-default behavior for both LTX2Pipeline and LTX2ImageToVideoPipeline. * Fix resolution-dependent timestep shift being a no-op in all LTX2 pipelines Every LTX2Pipeline variant's `mu = calculate_shift(...)` call passed the scheduler's `max_image_seq_len` config value as the `image_seq_len` argument instead of the current generation's actual packed sequence length. Since calculate_shift's formula is a line through (base_seq_len, base_shift) and (max_seq_len, max_shift), passing image_seq_len == max_seq_len always evaluates to exactly max_shift -- so `mu` was pinned to a constant (2.05 for the LTX-2.4 scheduler config) regardless of height/width/num_frames, even though `use_dynamic_shifting: true` is set specifically to make this resolution-dependent. Found while benchmarking LTX-2.4 diffusers output against the reference pipeline with bit-identical starting noise: the reference computes this shift from the real video token count (ltx_core's LTX2Scheduler.execute), which diverges substantially from the constant diffusers was using at any resolution other than exactly the checkpoint's max-anchor token count. For a 768x512, 121-frame video (6144 tokens), the reference lands on mu ~= 2.78 versus diffusers' constant 2.05. Fixed by passing the current call's actual packed video latent length (`latents.shape[1]`) as `image_seq_len`, matching the pattern already used correctly in pipeline_flux.py (the source this was copied from). Applies to all 5 LTX2 pipeline variants, each with their own independent `__call__` (not linked via `# Copied from` for this method). * Add LTX-2.4 duration head for automatic num_frames prediction LTX-2.4 checkpoints ship a small regression head (~1.9M params) that predicts the natural duration of the shot implied by a caption, from the same text connector output the transformer is conditioned on. With it converted, a caller can let the model choose the video length instead of picking `num_frames`. - duration_head.py: `LTX2DurationHead` (a `ModelMixin` optional pipeline component) plus the `LTX2AutoDuration` request object. Modality-specific projections map the video and audio connector streams into a shared pooler dim, learnable modality embeddings tag them, one learnable query cross-attends the concatenation, and a small MLP regresses a log-duration. `forward` returns seconds as a tensor; `predict_num_frames` clamps to bounds and snaps to the VAE's causal temporal grid. The attention pooler uses explicit to_q/to_k/to_v/to_out with `dispatch_attention_fn` rather than `torch.nn.MultiheadAttention`, which both reference implementations use because that is the layout the checkpoint ships. `nn.MultiheadAttention` is documented in diffusers as breaking `enable_sequential_cpu_offload`; the split form also gets backend dispatch. Two details are load-bearing for numerical parity: the GELU must be tanh-approximated (the exact GELU gives different numbers against the JAX-trained head), and the clamp must precede the grid snap (a clamped frame count is not necessarily grid-aligned). Where narrow bounds convert to a frame window containing no grid point -- at 24 fps [1.0s, 1.02s] rounds to [24, 24], and 24 is not 8k + 1 -- the nearest grid point is used and a warning logged, rather than refusing to generate over a rounding artifact. The output MLP's config argument is `mlp_hidden_dim`, not the reference's `mlp_hidden`: the submodule keeps the checkpoint's `mlp_hidden` name, and `ModelMixin.__getattr__` resolves config keys ahead of submodules, so the two colliding would shadow the `nn.Linear` with an `int`. - pipeline_ltx2.py / pipeline_ltx2_image2video.py: `num_frames` becomes `int | LTX2AutoDuration | None`. Omitting it auto-predicts when the checkpoint ships a head and keeps the legacy 121 otherwise, mirroring the reference -- whose CLI also defaults to auto-prediction -- and matching the resolution these pipelines already do for `enable_prompt_enhancement`, which likewise switches on the presence of an optional LTX-2.4 component. Pre-2.4 pipelines have no head, so nothing changes for them. The prediction runs immediately after the connectors and before `num_frames` is first read. Only the positive half of the CFG-concatenated batch is used, and rows past the first are `num_videos_per_prompt` duplicates. Auto-duration is rejected from `check_inputs` -- before prompt enhancement and encoding, so a bad request costs nothing -- when there is no head, and when more than one prompt is supplied: the batch carries a single temporal dimension, so prompts with different natural lengths cannot share one frame count. Batched prompts with an explicit integer `num_frames` are unaffected. - convert_ltx2_to_diffusers.py: `--duration_head` (with `--duration_head_prefix`) alongside the other per-component flags. The head's keys sit at the checkpoint top level rather than under the DiT prefix, so the existing prefix helper handles them. The checkpoint's fused `in_proj_weight` is split into separate q/k/v, and dimensions are read back from weight shapes since checkpoint metadata carries no duration_head config; only `num_pooler_heads` is not recoverable and is fixed at 4. Pre-2.4 checkpoints yield no keys and are skipped rather than failing. Verified against ltx_core on the real 2.4 checkpoint: fed the reference's recorded connector tokens, the converted head predicts 12.9375s (video only), 2.671875s (audio only) and 3.515625s (both) -- bit-identical to the reference -- and the same frame counts through the clamp/snap path at 24/25/30/8 fps. The snapping arithmetic matches the reference `seconds_to_clamped_num_frames` across 260 combinations of duration, frame rate and bounds. * Add LTX-2 modular video and audio decoder blocks Add the first blocks of the LTX-2 modular pipeline under modular_pipelines/ltx2/decoders.py: - LTX2VaeDecoderStep: unpacks and decodes video latents (or returns latents for output_type="latent"), applying the optional decode-time noise on normalized latents before denormalizing, matching the standard LTX2Pipeline decode stage. - LTX2AudioDecoderStep: unpacks and decodes audio latents into a waveform via the audio VAE and vocoder in a single block. Pack/unpack/denormalize helpers are redefined at module level rather than imported, since modular blocks must not import from diffusers.pipelines.* (the vocoder class is imported from the pipelines path for now, flagged for relocation to models/). Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com> * Add LTX-2 modular pipeline (t2v + i2v) and parity harnesses Add the LTX-2 modular pipeline package under modular_pipelines/ltx2/, covering the joint video+audio text-to-video and image-to-video workflows for LTX-2.4: - encoders.py: dedicated Gemma-4 prompt enhancer (t2v/i2v), Gemma text encoder, text connectors, and the i2v image VAE encoder. - before_denoise.py: text-input expansion, flow-match timesteps (with a deep-copied audio scheduler), video/audio latent prep, and RoPE coords. - denoise.py: the joint video+audio denoise loop with manual guidance (CFG + spatio-temporal + modality-isolation), shared across t2v/i2v. - decoders.py: video VAE decode and audio VAE + vocoder decode. - modular_blocks_ltx2.py: LTX2Blocks (t2v), LTX2ImageToVideoBlocks (i2v), and LTX2AutoBlocks (both, default), plus the auto/conditional wrappers. - modular_pipeline.py: LTX2ModularPipeline with the compression-ratio and patch-size properties the blocks read. Wire up lazy imports and register the pipeline (top-level diffusers exports, modular_pipelines __init__, MODULAR_PIPELINE_MAPPING, and dummy objects). Also add integrations/ (temporary, for-visibility) parity harnesses that compare the modular t2v/i2v blocksets against the standard LTX-2 pipelines by sharing the same loaded components. This directory is meant to be removed before the final integration. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com> * Add script to create tiny LTX-2.4 test pipeline ckpt (under assumption that it inherits all configs from LTX-2.3) * make fix-copies * Run modular connector once on CFG-concatenated batch for bitwise parity Run the LTX-2 text connector once on the CFG-concatenated `[uncond, cond]` batch (as `LTX2Pipeline` does) instead of once per branch, then split the outputs back into uncond/cond. The connector is applied per batch element, so both forms are mathematically equivalent, but its GEMM/attention kernels round identically for a given row only at batch >= 2; running the branches separately diverged from the standard pipeline by ~1e-6 at `num_videos_per_prompt=1`. The modular path is now bitwise-identical to the standard pipeline at any batch size. Also extend the T2V/I2V parity harnesses with a `--num_videos_per_prompt` argument and a `--check_tensor_stats` flag for per-output min/mean/std/max. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> * Use tiny LTX2VocoderWithBWE in the LTX-2.4 test checkpoint Swap the placeholder LTX2Vocoder for a scaled-down LTX2VocoderWithBWE that mirrors LTX-2.3's vocoder (snakebeta + antialiasing, no final activation/bias, 16kHz -> 48kHz bandwidth extension) while keeping the same in/out channel shapes. Dimensions are reduced but the shape invariants the two-stage forward requires are preserved: in_channels = audio_vae.output_channels * mel_bins, bwe_in_channels = out_channels * num_mel_channels, filter_length == window_length, and prod(bwe_upsample_factors) == (output_sr // input_sr) * hop_length so the BWE residual and the resampled stage-1 skip line up. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> * Match LTX-2.4 transformer flags in the test checkpoint Only `ff_bias=False` is a transformer-level delta from LTX-2.3 per the authoritative LTX-2.4 config in `scripts/convert_ltx2_to_diffusers.py`; `audio_ff_bias` and `use_prompt_adaln_single` keep their `True` defaults. The test checkpoint was incorrectly overriding both to `False`, so drop those two overrides. T2V/I2V modular-vs-standard parity remains bitwise. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> * Add CPU offload flag to parity scripts to be able to load full checkpoints * Support dynamic timestep shift and duration head in LTX-2 modular pipeline Track two recent additions to the standard LTX-2.4 pipelines in the modular blocks (t2v + i2v): - Resolution-aware timestep shift: LTX2SetTimestepsStep now computes `mu` from the actual packed video sequence length (derived from height/width/num_frames and the transformer patch sizes) instead of a constant, matching the standard pipeline's `latents.shape[1]`-based shift. Uses the compute-from-dims approach (like LTX-1 / Flux2), so no block reordering is needed. - Optional duration head: add LTX2DurationStep, which predicts a concrete `num_frames` from the connector text conditioning via the `duration_head` component when `num_frames` is an `LTX2AutoDuration` request, and re-emits it. Wrapped in the LTX2AutoDurationStep conditional (skipped for an integer `num_frames`) and wired into all three blocksets after the connector step, so `num_frames` is resolved before the shift and latent prep run. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com> * Add duration predictor support for tiny checkpoint and parity scripts * Refactor LTX-2 modular guidance into video/audio guiders Replace the manual multi-term guidance in `LTX2LoopDenoiser` with a `LTX2Guidance` guider (in `guider.py`), instantiated once as the video `guider` and once as the `audio_guider`. Each combines CFG + spatio-temporal guidance (STG) + modality-isolation via the delta formulation in x0 space; the denoiser owns a `plan_guidance_passes` union plan across the two guiders, runs each transformer pass, converts velocity->x0, and delegates the per-modality combine to the guiders. Guidance scales are now guider config, not `__call__` kwargs. Parity harnesses updated to configure the guiders accordingly. Parity investigation (not yet resolved): - The refactor runs every guidance pass as its own single-batch transformer forward, whereas the standard `LTX2Pipeline` batches the cond+uncond CFG pair into one forward and runs STG/modality-isolation as separate single-batch passes. STG and modality already match (single-batch in both). - The change is mathematically equivalent, not a logic bug: in fp32 the denoised latents match to ~8e-6 mean abs diff (sparse outliers up to ~3.5e-4), and disabling STG does not move the diff. - But GPU matmul is not batch-invariant, so cond computed alone differs from cond computed inside a batch-of-2. Negligible in fp32 (~1e-6/op); ~1e-2/op in bf16, where amplification by the CFG delta and accumulation over sampler steps drives the modular vs. standard bf16 latents to ~10% mean-relative divergence. - Net: numerical, but the modular pipeline does NOT reproduce the standard pipeline bitwise in bf16 (the real inference dtype). Restoring parity would require re-batching the cond+uncond pair into a single forward to match the reference execution, keeping STG/modality single-batch. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com> * Batch cond+uncond CFG forward to mirror standard LTX-2 pipeline Restore fp32 bitwise parity with `LTX2Pipeline` in the modular denoiser by running the cond+uncond CFG pair as a single batched transformer forward (`torch.cat([latents] * 2)` + `.chunk(2)`), keeping STG and modality-isolation as separate single-batch conditional forwards -- matching the reference op-for-op (batch sizes, repeated coords, cache-context names). `plan_guidance_passes` now emits forward-groups (`identifiers` / `conditioning` aligned lists + `flags` + `cache_context`) instead of one entry per pass; the denoiser runs each group once and chunks the CFG forward back into its `[uncond, cond]` identifiers. The `LTX2Guidance` combine is unchanged -- only how the four x0 tensors are obtained changed. Parity results: - fp32: bitwise (0.0 max abs diff), verified at full-checkpoint scale including under CPU offload. This is the authoritative parity gate. - bf16: the previous single-batch-per-pass design diverged ~10% mean-relative from the standard pipeline (GPU matmul is not batch-invariant: cond alone vs. cond in a batch-of-2). Batching the CFG pair removes that gap; a smaller ~1% (tiny) / ~5% (full) bf16 gap remains. It is not a logic difference (fp32 is bitwise across scale and offload); it is a bf16-kernel effect -- coarser mantissa amplifying non-associative accumulation order, plus bf16 using different kernels than fp32 (tensor-core GEMM algorithm selection, fused attention). bf16 is therefore a close-but-not-bitwise check, not a gate. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com> * Drive LTX-2 modular guidance through the guider API (per-pass inputs) Replace the batched-CFG denoiser with one that runs each guidance pass as its own single-batch transformer forward, driven end-to-end through the standard guider API. `LTX2Guidance.prepare_inputs(guider_inputs)` builds one identifier- tagged batch per active pass from a dict whose values are 4-tuples indexed by pass [cond, uncond, stg, modality]; the per-pass model flags (`spatio_temporal_guidance_blocks`, `isolate_modalities`) ride in those tuples alongside the encoder inputs, so a pass fully describes its own forward. The denoiser unions both guiders' passes by identifier, runs each once (storing video+audio x0 on the batch), and combines each modality via its guider's `forward`/`__call__`, filtered to that guider's active passes so the batch count matches `num_conditions`. Removes the bespoke `plan_guidance_passes` union helper and the empty-dict `prepare_inputs_from_block_state` call: the plan is now expressed as the `guider_inputs` tuples + `active_predictions()`, so guidance logic lives behind the guider API rather than in the denoiser. Parity trade vs. the previous batched-CFG design: - Batched CFG matched the standard pipeline op-for-op and was fp32-bitwise. Running every pass single-batch is mathematically equivalent but, since GPU matmul is not batch-invariant, cond computed alone differs from cond inside a batch-of-2: ~1e-4 mean-relative in fp32 on a full checkpoint (sparse outliers up to ~3.5e-4 max), ~10% mean-relative in bf16. - This is numerical, not a logic difference, and fp32-within-tolerance (not bitwise) is the modular-ecosystem norm. The trade buys end-to-end guider-API usage (swappable within the LTX-2 guidance family, per-pass flags carried the same way as encoder inputs) at the cost of the bitwise guarantee. Parity harnesses: gate on magnitude-aware stats (mean abs diff relative to mean magnitude, plus a loose max-abs ceiling) instead of assert_close's near-bitwise fp32 defaults, which no single-batch design can clear. fp32 is the authoritative gate (1e-3/1e-3); bf16 is a loose sanity check (0.15/0.5). `--atol`/`--rtol` become `--mean_rel_tol`/`--max_abs_tol`; motivation documented in-file. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com> * Drive LTX-2 modular guidance via prepare_inputs_from_block_state Move `LTX2LoopDenoiser` onto the standard Wan/Z-Image guider idiom: the denoiser now owns a `guider_input_fields` map (transformer arg -> per-pass block-state attribute names, indexed [cond, uncond, stg, modality]) and calls `guider.prepare_inputs_from_block_state(block_state, guider_input_fields)` instead of hand-building a literal `guider_inputs` dict in `__call__`. This lifts the cond/uncond/stg/modality field mapping to a construction-time arg (swappable per workflow) and resolves the connector_*->encoder_hidden_states name mismatch via the map keys. The two per-pass model flags (`spatio_temporal_guidance_blocks`, `isolate_modalities`) are pass-identity constants, not block-state conditioning, so they can't ride the name-referenced field map; the denoiser sets them on each batch by identifier after preparation, via a `pass_flags.get(identifier, (None, False))` lookup. The plain-conditional default keeps this correct for any guider that emits a subset of passes (e.g. a swapped-in `ClassifierFreeGuidance` -> just pred_cond/pred_uncond gets no STG and no modality isolation). `LTX2Guidance` gains `prepare_inputs_from_block_state` (names, via the base `_prepare_batch_from_block_state` helper); `prepare_inputs` (literals) is retained so both halves of the guider data-prep API are implemented. Pass structure and numerics are unchanged (still four single-batch forwards), so the fp32/bf16 parity story is untouched; user-confirmed parity OK. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> * Route LTX-2 batch-invariant denoiser kwargs via denoiser_input_fields Tag the three upstream-produced, batch-invariant transformer kwargs (`audio_num_frames` from the audio-latents step; `video_coords` / `audio_coords` from the coords step) with `kwargs_type="denoiser_input_fields"`, and have `LTX2LoopDenoiser` collect them from `block_state.denoiser_input_fields` filtered against the transformer's forward signature (à la qwenimage/cosmos3) instead of listing them as explicit inputs. This drops three explicit `InputParam`s in favor of one `denoiser_input_fields` template input. Per-pass conditioning (cond/uncond/stg/modality) stays on the guider field map -- the tag only delivers a flat dict, so it can't do the cond/uncond split or the connector_*->encoder_hidden_states rename. The locally-computed latent dims (num_frames/height/width/fps) are still supplied in-denoiser: they aren't upstream outputs and their names would clash with the pixel-space values in state. Parity unchanged (validated T2V + multi-frame I2V): the tagged values reach the transformer identically; the first-forward capture shows them bitwise-equal. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> * Fix LTX-2 parity harnesses: guidance overrides reach both pipelines The CLI guidance flags (`--guidance_scale`, etc.) only fed the modular guiders; the standard pipeline was always called with the hardcoded GUIDANCE dict. So `--guidance_scale 1.0` disabled CFG on the modular side only, comparing standard-with-full-CFG (batch-2) against modular-no-CFG (batch-1) -- an apples-to-oranges run that manifested as a huge (but spurious) I2V mismatch. Add `_resolve_guidance(args)` (CLI overrides on top of GUIDANCE) and drive BOTH the standard call and `_make_guiders` from the one resolved dict, in both the t2v and i2v harnesses. With CFG correctly disabled on both sides, multi-frame I2V is bitwise-ish (~5e-6 mean-rel), confirming the default-guidance ~8e-3 divergence is the documented cond/uncond batch-invariance (amplified by I2V's per-token masked timestep + clean anchor frame), not a logic bug. Also: - i2v: loosen the fp32 gate to (2e-2, 1.5e-1) to fit that amplified-but-numerical multi-frame divergence, with a comment pointing at the CFG-off run as the tight bug-catching gate. - i2v: add `--debug_forward`, which diffs the first transformer forward (inputs + outputs) between the two runs via a forward hook -- the diagnostic that pinpointed the batch-shape mismatch above. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> * Document denoiser_input_fields standalone-run caveat for LTX-2 denoiser `audio_num_frames` / `video_coords` / `audio_coords` reach `LTX2LoopDenoiser` via the `denoiser_input_fields` tag, not as named inputs. Note in the docstring that a standalone run (without the upstream tagging blocks) must pass them through `denoiser_input_fields={...}`; plain named kwargs are silently ignored (modular.md's kwargs_type standalone gotcha). Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> * Address LTX-2 modular self-review: fix dead enhancer trigger + docstrings Blocking fix: `enable_prompt_enhancement` was declared only as a `block_trigger_inputs` entry / `select_block` param, never as an `InputParam`, so it was not an accepted pipeline input -- `pipe(enable_prompt_enhancement=True)` was dropped as "unexpected" and the prompt enhancer could never run. Declare it on both enhancer sub-blocks so it reaches `select_block` (mirrors how the `image` trigger is declared). Also from the self-review: - Regenerate the modular auto-docstrings: the guidance knobs (guidance_scale, stg_scale, ...) that moved onto the guider no longer show as block inputs, and the enhancer trigger now appears. - Add descriptions to the 16 `InputParam`s that rendered as "TODO: Add description." in the generated docstrings (conversion checklist requires none). - Drop the defensive `getattr(tokenizer, "padding_side", "left")` (a declared tokenizer always has it; gotcha #7). - Rewrite two ephemeral comments (the connector-output "reconcile when denoise.py is written" NOTE, now resolved; the guider "batched-CFG variant in git history" pointer) into standing rationale. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> * Fix stale I2V parity-harness --help text for the loosened fp32 gate The `--mean_rel_tol` / `--max_abs_tol` help strings still advertised the old fp32 defaults (1e-3, 1e-3); the I2V gate is now (2e-2, 1.5e-1). Update the help to match the actual DTYPE_TOLERANCES so `--help` doesn't misreport the gate. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> * make style and make quality * Add the LTX-2.4 diffusion VAE decoder with a native-parity harness * Add a converter for the LTX-2.4 diffusion VAE decoder * Initialise use_slicing and document the diffusion VAE decisions * Record real-weight parity against the reference decoder * Add model-level tests for the LTX-2.4 diffusion VAE decoder The generated test file needed three decisions rather than fill-ins: the class had no forward() for the mixins to call, the decoder denoises so forward has to take a generator for any output comparison to mean anything, and MemoryTesterMixin.test_group_offloading reused one inputs_dict across four forwards without re-seeding it. The last is fixed in the mixin, reusing the helper test_group_offloading_with_disk already had for the same reason, now module-level and reading the signature off the class (offloading replaces model.forward with a *args wrapper). * Fold the diffusion VAE converter into convert_ltx2_to_diffusers.py --diffusion_vae now sits beside --vae instead of shipping a second script. It also drops the standalone script's --encoder-vae: the encoder is in the same checkpoint and goes through the conv VAE's own rename rules, with its config pinned in get_ltx2_diffusion_video_vae_config. Output verified bitwise identical to the standalone script's on the rc2 checkpoint, 491/491 tensors and the same config.json. * Make the diffusion decoder work through LTX2Pipeline The documented usage -- LTX2Pipeline.from_pretrained(repo, vae=diffusion_vae) -- had never been run: every real-weight run so far called vae.decode() directly. Through the pipeline it raised on vae.config.timestep_conditioning, which this decoder has no reason to carry, and would have bound the positional decode timestep to the decoder's generator. The decode step now branches on the decoder type, skipping the decode_timestep pre-noising and passing the generator instead, which also makes decoding seed-reproducible; two full runs from one seed agree bitwise. The conv path's own statements are unchanged. * Make the diffusion decoder work through the modular decode step Same fix as the standard pipeline, in LTX2VaeDecoderStep: skip the decode_timestep pre-noising and pass the generator instead of a timestep. Verified on rc2 weights by injecting the decoder into LTX2Blocks().init_pipeline() with update_components, the route the modular parity harness already uses -- two runs at 320x448x17 from one seed agree bitwise, so no modular_model_index.json repo was needed to run this. * Note that the pipeline decode block predates the LTX-2.4 integration PR * Address diffusers self-review on the diffusion VAE decoder Four things the project's own rules catch: - models.md forbids unconditional torch.float64 in a model (MPS/NPU/Neuron cannot run it). The RoPE frequency base now goes through maybe_adjust_dtype_for_device, the helper flux/flux2/wan use for exactly this. Measured cost of the downcast where it applies: 1.5e-08 on the frequencies, 1e-06 on the angles. - rope_dim_split was threaded through five classes but was never a config entry, so it was always None and always fell back to the default split. Removed, and the default-split helper inlined into its one caller. - FromOriginalModelMixin was declared with no SINGLE_FILE_LOADABLE_CLASSES entry, so from_single_file raised rather than working. Dropped; single-file support can come with its own mapping later. - set_attention_backend() overwrites the processor's _attention_backend, which handed the neighborhood BlockMask to backends that cannot read it. Guarded like AnyFlowCausalAttnProcessor does. Also runs make fix-copies, which was missing the dummy object for the new class. * Add the API doc page for AutoencoderKLLTX2VideoDiffusionDecoder * Mark the parity harness transient and drop the notes doc from the diff Matches the header the other integrations/ harnesses on this branch already carry, and states that the file imports the native reference package. The notes doc goes to the PR description instead: the self-review skill is explicit that it never ships in the diff. * Accept the diffusion decoder in the image-to-video pipeline too Same branch as the text-to-video pipeline: skip the decode_timestep pre-noising and pass the generator instead of a timestep. The remaining LTX2 pipelines that share this decode block (condition, hdr_lora, ic_lora, latent_upsample) are deliberately left for later, so the surface stays the two pipelines this PR actually exercises. * Reorganize LTX-2 modular blocks into coarser component-aligned phases Regroup the top-level LTX-2 block assemblies so each direct child of LTX2AutoBlocks is a coherent, component-aligned phase, mirroring Flux 2's [text_encoder, vae_encoder, denoise, decode] shape: - New LTX2TextConditioningStep wraps [text_encoder, text_input, connectors] as one "text_encoder" phase (LTX-2's text conditioning is genuinely a three-step model chain; text_input must precede connectors for batch-invariant parity, so the whole chain lives here rather than pushing text_input into denoise). - New LTX2DecoderStep wraps [video_decode, audio_decode] as one "decode" phase. - duration stays a top-level child: it is component-aligned (duration_head) and a ConditionalPipelineBlocks that self-skips for concrete num_frames, so it is a cleanly optional phase alongside prompt_enhancer / vae_encoder -- keeping it out of the (mandatory) denoise block. Top-level children become: t2v: [text_encoder, duration, denoise, decode] i2v: [text_encoder, duration, vae_encoder, denoise, decode] auto: [prompt_enhancer, text_encoder, duration, vae_encoder, denoise, decode] Also reorder the class definitions to follow this flow, keeping the core-denoise trio (LTX2CoreDenoiseStep, LTX2Image2VideoCoreDenoiseStep, LTX2AutoCoreDenoiseStep) contiguous instead of split by LTX2AutoVaeEncoderStep. Pure re-grouping: no block bodies change and intermediate outputs still propagate, so t2v/i2v parity is bit-identical to before (user-confirmed at 17 frames). Docstrings regenerated. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> * Enable LTX-2 prompt enhancement by default when the enhancer is loaded Mirror the standard pipeline's tri-state prompt-enhancement default (pipeline_ltx2.py:559-560), where `enable_prompt_enhancement` defaults to auto-on when a `prompt_enhancer` component is present (LTX-2.4) and off otherwise, and wire the enhancer into the t2v/i2v assemblies. - Both enhancer sub-blocks: default `enable_prompt_enhancement=None` (tri-state). Resolve `None` against component presence inside `__call__` -- select_block cannot see components, so the gate dispatches for None/True and the sub-block decides. `None` + no enhancer -> pass the prompt through unchanged (the Cosmos3 optional-component pattern); explicit `True` + no enhancer -> a clear ValueError instead of the previous cryptic `NoneType` crash from within the enhance helper. - LTX2AutoPromptEnhancerStep.select_block: skip only on an explicit `False`. - Add LTX2AutoPromptEnhancerStep to LTX2Blocks and LTX2ImageToVideoBlocks so all three assemblies share the prompt_enhancer-first shape (previously only LTX2AutoBlocks had it; passing the flag to the others was silently ignored). - Parity harnesses: force `enable_prompt_enhancement=False` on the modular run too (the modular sets now carry an enhancer), and fix the now-stale "contains no enhancer block" docstrings. Only the dedicated-enhancer (LTX-2.4) path is wired; the standard pipeline's text_encoder-as-enhancer fallback for LTX-2.0/2.3 remains a follow-up. Parity unchanged (both pipelines run with enhancement disabled in the harnesses). Docstrings regenerated. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com> * Rename LTX-2.4 product identifiers to LTX-2.5. Update conversion --version, model ids, system-prompt constant names, and docs/comments to the public 2.5 name. Behavior is unchanged in this commit. * Add image-conditioning H.264 CRF matching Lightricks training. Resolve CRF 18 for LTX-2.5 (Gemma 4) and 33 for earlier generations, and apply the PyAV re-compress path for I2V and single-frame Condition/IC keyframes. * Align LTX-2 pipelines with the Lightricks reference behavior. Extract shared prompt-enhancement and check_inputs mixins; enable Condition duration+enhancement and IC enhancement (HDR remains encode-only); match enhancement recipe and LTX-2.3/2.5 sampling defaults. * Update LTX-2 docs for 2.5 naming, defaults, and opt-in enhancement. Document LTX_2_3/2.5 sampling defaults, STG block 28, and enable_prompt_enhancement=True as the opt-in path. * Replace LTX2AutoDuration with min_seconds/max_seconds call args. Drop the dataclass wrapper and expose duration bounds directly on the T2V, I2V, and Condition pipelines. * Align LTX-2 modular blocks with the merged standard-pipeline changes The standard LTX-2 pipelines moved to shared `LTX2PromptEnhancementMixin` / `LTX2CheckInputsMixin`, dropped `LTX2AutoDuration`, adopted the Lightricks reference defaults, and gained H.264 CRF re-compression of image conditionings. Port all of that to the modular blocks. - Prompt enhancement: re-derive `_enhance_prompt` from the new mixin -- the `user prompt:` / `User Raw Input Prompt:` templates, 896px long-side image prep, left-padding to a multiple of 8 for Flash Attention, `clean_response` on the decoded output, and `max_new_tokens=None` resolving to the Gemma-4 budget of 600. - Revert `enable_prompt_enhancement` to a plain `False` opt-in, matching the reference pipelines (the tri-state auto-on default is gone upstream). The friendly error for `True` with no enhancer loaded is kept. - Auto-duration: trigger on an omitted `num_frames` instead of an `LTX2AutoDuration` sentinel, with `min_seconds`/`max_seconds` as call args. `LTX2DurationStep` raises when no `duration_head` is loaded rather than silently falling back to 121 frames. - Every `num_frames` InputParam default becomes `None`: input defaults are seeded into the pipeline state before any block runs, so a default of 121 would leave the auto-duration branch permanently unreachable. - Defaults sweep: `num_inference_steps` 40 -> 30, `use_cross_timestep` False -> True, and the video/audio guider ComponentSpec configs updated to the reference guidance stack. - `LTX2VaeEncoderStep` gains `image_crf` and re-compresses the conditioning image before preprocess, declaring `text_encoder` only to resolve the model default CRF. - Rename LTX-2.4 -> LTX-2.5 throughout, following the upstream product rename. Parity harnesses updated for the new duration arguments, plus an `--image_crf` flag on the i2v harness defaulting to 0 so the comparison isolates block logic from the PyAV codec round-trip. Verified against a real checkpoint: t2v, i2v at `--image_crf 0`, and i2v at `--image_crf -1` all pass. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> * Evaluate the decoder's SwiGLU in token tiles Decode-only peak VRAM at 121 frames and 512x768 was 24.6 GiB, and 17.0 GiB of that was one transient inside the first stage-5 block: `w_gate(x)` and `w_up(x)` are both hidden-width and their product makes a third, so the whole video's worth of hidden activations was live three times over. At that size each one is 2,973,696 tokens x 1024 x 2 bytes = 5.67 GiB. The MLP is pointwise across tokens, so tiling it is exact -- it changes only how many hidden-width elements exist at once. Measured on a full-size decode: peak 24.8 -> 19.4 GiB (-22%), wall clock 2.79 -> 2.84 s (+1.6%), output bit-identical (max abs diff 0.000e+00). That also puts the diffusion decoder below the conv decoder, which needs 23.8 GiB at the same size. Tile size 16384 tokens is the reference decoder's own default (`DEFAULT_SWIGLU_TILE_SIZE`). Bounding a token count rather than a number of tiles keeps peak memory independent of resolution. This is the first of the two transients the reference's default decode mode avoids; the other is the full-volume QKV projection plus RoPE's fp32 upcast, which it addresses by chunking attention along width. That one is not bit-exact (it reassociates NATTEN's accumulation), so it is left for a follow-up rather than changed here. * Declare _no_split_modules on the diffusion decoder Both block types close over a residual add that combines outputs from different children, which is the case models.md says has to stay co-located, so neither can be split across devices. Unskips three memory tests that were gated on the attribute: the file goes from 35 passed / 7 skipped to 38 passed / 4 skipped, and the three (test_cpu_offload, test_disk_offload_with_safetensors, test_disk_offload_without_safetensors) pass. * Match the encoder defaults to the published LTX-2.4 config block_out_channels was (256, 512, 1024, 2048) and layers_per_block was (4, 6, 6, 2, 2); both were inherited from the 2.0 conv VAE. The published vae_diffusion/config.json has (256, 512, 1024, 1024) and (4, 6, 4, 2, 2). Real loads were unaffected because the config sets these explicitly, but the defaults described a model that does not exist. All 27 __init__ defaults that appear in the published config now match it. * Cover the token-tiled SwiGLU path in the tests The dummy video is 9x48x48, so its stage-5 grid is 5184 tokens against a 16384-token tile size: every other test in the file takes the untiled branch and the tiling loop ran nowhere in CI. This shrinks the tile size to force ~41 tiles and requires torch.equal against the untiled evaluation, since the MLP is pointwise across tokens and tiling must be exact rather than close. Checked the test is not vacuous: sabotaging the tiled branch alone (silu on w_up instead of w_gate) fails it at 8.83e-01. * Let the parity harness run against the LTX-2.5 reference too The harness only spoke LTX-2.4's decoder API and died on `forward_pre_diffusion` against 2.5, so it could not check the release the port is now targeted at. Three shims absorb the differences: * 2.5 selects a decode pathway by swapping `__class__` on every block, so an as-constructed decoder has no `forward_combined`. Install the COMBINED pathway explicitly, uncompiled, since that is the pathway this port implements. * stages 1-4 split into `forward_stages_1_to_3` + `forward_stage_4`, so the chunked pathway can defer stage 4. * the trailing NATTEN ghost pad moved out to the caller while its crop stayed behind `forward_stage_4(pad_trailing=True)`; the two have to be paired or the context loses real frames (3 of 17 survive at this config, which is how the mismatch first showed up). Same numbers against both references -- context 5.367e-04, step 7.337e-04 -- which is the check that the shims are semantically right and not just shape-compatible. * Add LTX-2.X modular condition blocks Ports LTX2ConditionPipeline to the modular pipeline system, including the LTX-2.5 additions (per-condition CRF, conditions-sourced prompt enhancement, auto-duration, the Lightricks reference defaults). New blocks: - encoders.py: LTX2ConditionEncoderStep (resize/center-crop, single-frame H.264 re-compression at the model CRF, temporal trim, VAE encode) and LTX2ConditionPromptEnhancerStep (grounds the rewrite in the first PIL frame found in `conditions`, text-only otherwise). - before_denoise.py: LTX2ConditionPrepareLatentsStep (first-frame overwrite + keyframe token append with their own RoPE coords, emitting conditioning_mask / clean_latents / appended_coords / base_token_count), LTX2ConditionSetTimestepsStep, LTX2ConditionPrepareAudioLatentsStep, LTX2ConditionPrepareCoordsStep, and the _prepare_keyframe_coords helper. - denoise.py: LTX2ConditionLoopBeforeDenoiser (mask-scaled per-token video timestep), LTX2ConditionLoopAfterDenoiser (x0 blend against the clean condition latents, then a full-sequence scheduler step), LTX2ConditionDenoiseStep. - decoders.py: LTX2TrimConditionTokensStep. - modular_blocks_ltx2.py: LTX2ConditionAutoPromptEnhancerStep, LTX2ConditionCoreDenoiseStep, LTX2ConditionDecoderStep, LTX2ConditionBlocks. LTX2LoopDenoiser is reused unchanged: the two LTX2Guidance guiders already express the whole CFG + STG + modality-isolation stack the condition pipeline uses, and the transformer takes the longer packed sequence with the base num_frames/height/width exactly as the standard pipeline does. The standard pipeline's CFG batch duplication (conditioning mask, coords) has no modular counterpart, since each guidance pass is its own single-batch forward. Block ordering: prepare-latents runs *before* set-timesteps, unlike the text-to-video and image-to-video core denoise steps. The resolution-aware shift `mu` is computed from the packed latent sequence length, which here includes the appended keyframe tokens, so the latents must exist first. This mirrors LTX2ConditionPipeline (its section 4 precedes section 5). The text-to-video and image-to-video blocksets are unaffected: with no appended tokens the grid-derived sequence length already equals latents.shape[1]. Two subtleties the parity harness surfaced: - The condition pipeline samples audio noise directly in packed shape [B, L, C * M], while the text-to-video and image-to-video pipelines sample unpacked [B, C, L, M] and pack afterwards. Both draw the same number of values from the generator but lay them out differently, so reusing the shared LTX2PrepareAudioLatentsStep silently desynchronizes the audio noise and, through the joint attention, the video too (1.4 mean-rel on audio, 0.13 on video before the fix). Hence a standalone condition audio block. - `noise_scale` means different things across workflows: 0.0 for text-to-video/image-to-video, `None -> sigmas[0] or 1.0` for conditions. A blockset keeps the first non-None default across its blocks, so a 0.0 would have shadowed the condition resolution and left the latents unnoised. Both condition-path blocks declare None; prepare-latents resolves once and writes the value back for the audio step. Keyframe tokens, masks and coords are expanded to the generation batch (the pattern the in-context pipeline already uses for reference tokens). The standard pipeline builds them at batch 1 and cats them onto a batch-B sequence, so it raises for num_videos_per_prompt > 1 with any condition at latent index > 0; the modular blocks handle that case. Verification: integrations/ltx2_condition_parity.py (transient, removed before merge) compares LTX2ConditionBlocks against LTX2ConditionPipeline on shared component objects. Eight cases on a tiny checkpoint -- first-frame only, keyframe only, both plus a multi-frame video condition, two keyframes, no conditions, --crf -1, --predict_duration, num_videos_per_prompt=2 -- all pass at 3e-7 to 1.3e-6 mean-rel. On a full checkpoint at 768x512x17 with two conditions through the CRF path: video 8.7e-04 mean-rel / 1.1e-02 max-abs, audio 1.5e-04 / 2.1e-03, in line with the image-to-video figures at the same frame count. make style, make quality and make fix-copies are clean; auto-docstrings regenerated with no TODO placeholders. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> * Add LTX-2.X modular in-context (IC-LoRA) blocks Ports LTX2InContextPipeline to the modular pipeline system on top of the condition blocks, and fixes two bugs in the standard in-context pipeline that the parity harness surfaced. New blocks: - encoders.py: LTX2ReferenceEncoderStep (preprocess, VAE-encode and pack each reference video, compute the coords that map its tokens into the target space, and build the per-token cross-attention strengths), plus the _downsample_mask_to_latent helper. - before_denoise.py: LTX2InContextPrepareLatentsStep (frame conditions as in the condition step, then the reference tokens appended last) and LTX2BuildVideoSelfAttentionMaskStep. - modular_blocks_ltx2.py: LTX2AutoReferenceEncoderStep, LTX2AutoBuildVideoSelfAttentionMaskStep, LTX2InContextCoreDenoiseStep, LTX2InContextBlocks. LTX2ConditionDenoiseStep is reused unchanged: with the blend gate fixed below, reference tokens are pinned by exactly the same x0 blend as frame conditions, matching the reference implementation where VideoConditionByReferenceLatent and VideoConditionByKeyframeIndex produce the same (denoise_mask, clean_latent) pair and post_process_latent runs unconditionally. The condition encoder, timesteps, audio-latents, coords and decoder blocks are shared as well. video_self_attention_mask reaches the transformer through the denoiser_input_fields tag, so LTX2LoopDenoiser needed no change. `reference_conditions` is optional, matching LTX2InContextPipeline: IC-LoRAs that carry their behavior in the adapter weights (camera control, style) take no reference video, which is the shape of the standard pipeline's own docstring example. The reference encoder and the attention-mask step are both skipped when it is absent. There is no duration step (the in-context pipeline ships without a duration_head), so LTX2ConditionEncoderStep now raises a concise error if `num_frames` is still None by the time the conditions are encoded. Per-reference token counts come from the encoder rather than an equal split of the total, so references of differing lengths (a reference video shorter than num_frames) get the right strengths. Standard-pipeline fixes in pipeline_ltx2_ic_lora.py: - The x0 blend was gated on `has_conditions` alone, so with reference conditions and no frame conditions the reference tokens were seeded clean and given a zeroed timestep but never re-pinned. Their x0 prediction error, divided by sigma each step, then accumulated and drifted them away from the encoded reference. Now gated on `has_conditions or num_ref_tokens > 0`, in line with the surrounding gates and the reference implementation. - video_self_attention_mask was rebound in the loop rather than expanded into a per-pass local. The main pass expanded it to the CFG-doubled batch, after which the STG pass's expand() to `latents.shape[0]` raised "RuntimeError: The expanded size of the tensor (1) must match the existing size (2)". Any run combining an attention mask with STG or modality guidance -- i.e. the default guidance settings -- died on the first step. Also removed the unused has_appended_tokens local and replaced the "# - TODO" placeholder above the attention-mask construction with the block structure, which the reference confirms. Verification: integrations/ltx2_in_context_parity.py (transient, removed before merge). Twelve cases on a tiny checkpoint -- reference only, reference at partial strength, scalar attention strength, pixel-space attention mask, downscale factor 2, references plus first-frame and keyframe conditions, two references, the CRF path, and four reference-free variants -- all pass at 3.4e-7 to 1.3e-6 mean-rel. The seven-case condition suite still passes. On a full checkpoint at 768x512x17 with a reference plus two conditions: video 4.4e-05 mean-rel / 5.6e-04 max-abs, audio 3.2e-05 / 2.4e-04. Known limitation, not addressed here: transformer_ltx2.py converts the multiplicative [0, 1] self-attention mask to an additive bias linearly, as (1 - mask) * -10000, whereas the reference uses log space (bias = log(mask), finfo.min at zero). Intermediate strengths therefore saturate to "fully masked", making conditioning_attention_strength effectively binary and spatially varying masks inert beyond their zero/non-zero pattern. Parity is unaffected -- both pipelines feed the same mask into the same transformer -- but the feature does not currently work as documented. make style, make quality and make fix-copies are clean; auto-docstrings regenerated with no TODO placeholders. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> * Make the diffusion decoder a decode pipeline instead of a VAE Addresses the review: a full diffusion model should not be an AutoencoderKL that hides its denoising behind `.decode()`, and it should not have to be threaded into every LTX-2 pipeline as a `vae`. AutoencoderKLLTX2VideoDiffusionDecoder becomes LTX2VideoDiffusionDecoderModel, a plain ModelMixin with no encoder. Encoding stays with AutoencoderKLLTX2Video, whose latent space this consumes unchanged, so latents remain interchangeable between the two decoders. Dropping the encoder also removes the converter's awkwardness of sourcing encoder weights and the real block_out_channels from the conv `vae/` folder: ten encoder-only config keys are gone. LTX2VideoDiffusionDecodePipeline drives it, shaped like LTX2LatentUpsamplePipeline: run any LTX-2 pipeline with output_type="latent", then decode. `vae` is an optional component, since it is only ever consulted for the latent statistics, and the decoder carries its own `latents_mean` / `latents_std` buffers to fall back on. That means a decode-only workflow never loads a second autoencoder. The `vae=` path is removed accordingly: the isinstance branches in LTX2Pipeline, LTX2ImageToVideoPipeline and the modular decode step are gone, along with the fixtures that built a diffusion decoder to pass as `vae`. The model's slicing/tiling test class went with them, since enable_tiling was an AutoencoderMixin concern and this is no longer an autoencoder. Tests: 37 passed / 3 skipped on the model, 83 passed / 2 skipped across the t2v and i2v pipelines. Still to come: mapping the 2.5 checkpoint to a blockset that selects the diffusion decode block, and the KandinskyCombinedPipeline pattern for running the two-step flow by default in the standard API. * Add a modular decode block for the LTX-2 diffusion decoder The previous commit removed the `isinstance(vae, ...)` branch that let the diffusion decoder stand in as the modular `vae`, which was the right call twice over: it is what the review objected to, and modular.md says a new case gets a new block rather than a branch inside an existing one. But removing it without a replacement left modular with no route to the diffusion decoder at all. LTX2DiffusionVaeDecoderStep is that replacement. It declares the decoder as its own `diffusion_decoder` component rather than borrowing the `vae` slot, and passes a generator instead of a decode timestep, since this decoder draws the noise it denoises. `LTX2VaeDecoderStep` is untouched, so the convolutional path is unaffected. What is still missing is the wiring: a blockset using this block, and an `_ltx2_map_fn` so a checkpoint that ships the diffusion decoder selects it automatically instead of the user choosing. That lands in modular_blocks_ltx2.py, which #12 is reorganizing, so it needs sequencing against that PR rather than racing it. * Test the diffusion decode pipeline, and give it a video-only output The decode pipeline had no coverage: it was never actually run. Writing the tests immediately turned up a bug, which is that it returned `LTX2PipelineOutput`, whose `audio` field is required. This pipeline decodes video only, so it now returns a video-only `LTX2VideoDecodeOutput` instead of passing a meaningless `audio=None`. Four tests: decode with no `vae` (the fallback to the decoder's own latent statistics), decode with a `vae` supplied (its statistics take precedence, checked by making the two disagree rather than asserting a shape), reproducibility under a seeded generator plus divergence under a different seed, and `denormalize=False` actually skipping the statistics. The decoder's stat buffers are set to non-trivial values in the fixture so a run that silently skipped denormalization could not pass by coincidence. * Fix the decode example: output_type="latent" is already denormalized The example in the docs and the pipeline docstring both showed `output_type="latent"` feeding straight into the decode pipeline on its defaults. That path denormalizes twice: `LTX2Pipeline` applies the latent statistics before returning latents (pipeline_ltx2.py), and the decode pipeline applies them again because `denormalize` defaults to True. Every channel ends up scaled by its own std a second time, so e.g. channel 0 (std 0.238) comes out roughly 4x too small. Passing `denormalize=False` in the example and saying so in both docstrings. Caught by running the flow end to end on real rc4 weights, which is also where the two decoders agree at 0.9978 once the statistics are applied only once. Whether the *default* should flip, or `output_type="latent"` should stop denormalizing instead, is a contract question across both pipelines and is still open. * Fix IC-LoRA video self-attention mask grouping The video self-attention mask deviated from the reference implementation (`ltx_core.conditioning.mask_utils.build_attention_mask`) in two ways. Both predate the modular blocks and applied to `LTX2InContextPipeline` as well; the modular block had ported the same construction. 1. Keyframe conditions cross-attended with reference tokens. `num_noisy_tokens` was derived as `latents.shape[1] - num_ref_tokens`, which folds the appended keyframe tokens into the noisy group, so they received the reference cross mask. The reference takes `num_noisy_tokens` from the target latent shape -- generated-video tokens only -- and tracks the extras offset separately, so keyframe <-> reference is 0.0. Split the two quantities apart: `_build_video_self_attention_mask` now takes `num_prefix_tokens` alongside `num_noisy_tokens`. 2. Multiple reference conditions fully attended to each other. All references were passed as a single attention group with a 1.0 self-block. The reference wraps each `LTX2ReferenceCondition` in its own `ConditioningItemAttentionStrengthWrapper`, building the mask once per item, so reference_i <-> reference_j is 0.0. The call site now splits `ref_cross_mask` into one group per reference before building the mask. Threading per-reference token counts out of `_encode_reference_conditions` also removes the equal-split assumption in `prepare_latents` and `prepare_reference_latents`, which assigned the wrong per-token strengths when references encoded to different token counts (reachable when a reference video is shorter than `num_frames`). API impact ---------- `prepare_latents` returns a 7-tuple instead of a 6-tuple, adding `ref_token_counts` (`list[int]`) as the new final element. Elements 1-6 keep the types they have on `main`; in particular `ref_cross_mask` remains the concatenated `[1, num_ref_tokens]` tensor. Callers that unpack the tuple fail immediately with a `ValueError` rather than silently receiving a changed type. `_encode_reference_conditions` (private) likewise gains `reference_token_counts` as a fourth return element. `prepare_reference_latents` keeps its documented 4-tuple unchanged. Verification ------------ Correctness against the reference. Both the standard helper and the modular block were checked for exact tensor equality (`torch.equal`) against `build_attention_mask`, driven the way `ic_lora.py` drives it -- one `ConditioningItemAttentionStrengthWrapper` per reference, so the reference builds iteratively with `existing_mask` carried forward. Five layouts, all matching, exercised through the same concatenate-then-split path the call site uses: - references only, 1 reference - keyframes + 1 reference (exercises fix 1) - keyframes + 2 references (exercises fixes 1 and 2) - 2 references of unequal length (exercises fix 2 and the token counts) - no keyframes, 3 references (exercises fix 2) Standard/modular parity on a real checkpoint, 512x512x17, fp32, via `integrations/ltx2_in_context_parity.py`. Video latents (1, 128, 3, 16, 16), audio latents (1, 8, 18, 16); gates are mean-rel 2e-2 and max-abs 1.5e-1: --reference 1.0 9 --condition 2 0.5 9 --conditioning_attention_strength 0.5 video: max abs 4.822e-05, mean rel 7.851e-06 audio: max abs 1.875e-04, mean rel 1.773e-05 --reference 1.0 9 --reference 0.8 9 --conditioning_attention_strength 0.5 video: max abs 1.953e-04, mean rel 9.101e-05 audio: max abs 9.251e-05, mean rel 1.026e-05 The first case is the layout where `num_prefix_tokens != num_noisy_tokens`; a wrong prefix/base split would have placed the group blocks at the wrong offsets with valid shapes, surfacing as a parity mismatch. The returned video shape also unpacks from exactly 768 base tokens (3 x 16 x 16), confirming `base_token_count` is the quantity now fed as `num_noisy_tokens`. Scope of the parity runs: both sides share this construction, so parity shows they did not desynchronize, not that either matches the reference -- that rests on the equality test above. Both references in the second case are 9 frames and so encode to equal token counts, meaning the equal-split and per-count paths coincide; the token-count change is not discriminated by these runs. A reference pair of differing lengths (e.g. `--reference 1.0 9 --reference 0.8 17`, giving 512 vs 768 tokens) would separate them, and would have failed parity before this commit since the modular block already used per-reference counts while the standard pipeline split evenly. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> * Add LTX25AutoBlocks and LTX25ModularPipeline Following the review: LTX-2.5 is a new checkpoint, so it gets its own blockset and pipeline rather than a config flag inside the LTX-2 ones. LTX25AutoBlocks subclasses LTX2AutoBlocks and overrides exactly one entry, `video_decode`, to LTX2DiffusionVaeDecoderStep. Every other leaf block is reused, so the two blocksets have identical block_names and cannot drift apart. That makes the diffusion decoder the default for LTX-2.5, which matches what the checkpoint ships natively, without the user having to pass a decoder at all. Going the other way stays a one-line swap rather than a second official blockset: blocks.sub_blocks["video_decode"] = LTX2VaeDecoderStep() LTX25ModularPipeline carries `default_blocks_name = "LTX25AutoBlocks"` and a new "ltx2.5" key in MODULAR_PIPELINE_MAPPING, so a repo shipping `modular_model_index.json` routes straight to the new blockset. The condition and in-context workflows belong in this blockset too, but those blocks live in the modular condition/IC PR, so folding them in belongs there rather than as a competing change here. * Drop the encoder half in the diffusion decoder converter The converter still assembled the whole VAE checkpoint, encoder included, and handed it to a strict `load_state_dict`. That was correct while the class was an autoencoder; after it became decoder-only the ~84 `encoder.*` keys have nowhere to land and the load raises. Nothing caught it because no test converts anything and every other check loads pre-converted weights, where unexpected keys are only warned about. Now the encoder is discarded rather than remapped, keeping the `decoder.` half and the per-channel statistics that become `latents_mean` / `latents_std`. `strict=True` stays, since it is what guards against a botched rename rule. Verified by actually running it: pulled the 395 `vae.*` tensors out of the native rc4 checkpoint by byte range, converted, and diffed against the already-published folder. 407/407 parameters, max abs difference 0.000e+00, so the fix changes nothing about the weights it produces. Also added a regression test, since the absence of any converter coverage is why this slipped. * Share the neighborhood attention mask and parameterise the AdaLN chunk count Two of the resolved review threads. Both are internal to the decoder modules and are unaffected by the pipeline-vs-model question still open on the thread above them. Build the FlexAttention mask once per stage instead of once per block. The mask depends only on the grid and the kernel, both fixed within a stage, so 24 builds collapse to 5; measured at 768x512x121 that is 582ms to 132ms. build_block_mask returns None for NATTEN, which encodes the window in its kernel. That is not merely an optimisation: create_block_mask materialises O(N^2) uncompiled, so a 69x64x96 stage would ask for 167 GiB and stage 5 for 8.2 TiB, and the mask must never be built for a path that would not read it. Make the AdaLN chunk count a constructor argument, num_chunks on the shared AdaLN and num_mod_params on the diffusion block, with the decoder passing shared_adaln.num_chunks through so the two cannot drift. num_mod_params is already the name LTX2AdaLayerNormSingle uses. The block's forward still destructures exactly seven chunks and reads four of them, which is the reference's shape. Decoding the test fixture is bitwise identical to before (max abs diff 0.000e+00). 39 passed, 4 skipped. * Export the LTX-2.5 modular classes from the top-level namespace `ModularPipeline.from_pretrained` resolves a repo's `_class_name` with `getattr(importlib.import_module("diffusers"), class_name)`, so a class that is only reachable from `diffusers.modular_pipelines.ltx2` cannot be selected by a checkpoint. `LTX25ModularPipeline` and `LTX25AutoBlocks` were exported there but not from `diffusers` itself, which left the whole checkpoint-to-blockset mapping dead: loading a repo whose index names them raised `AttributeError: module diffusers has no attribute LTX25ModularPipeline`. Exported alongside `LTX2ModularPipeline` / `LTX2AutoBlocks`, which is how the loader already …