LTX-2.5 first-and-last-frame — the config that actually works

Extracted from video_ltx2_5_flf2v fresg.json, the workflow Radek confirmed produces good output. Recorded because getting this wrong looks like a broken model rather than a wrong preset.

The trap

There are two LTX-2.5 transformers and they need opposite sampling regimes. Running one at the other's settings produces soft, washed-out, distorted frames that read as a bad model or bad anchors. It is neither.

	distilled (what the preset uses)	dev
transformer	`ltx-2.5-22b-distilled-transformer-comfy-int8-convrot`	`ltx-2.5-22b-dev-transformer-bf16`
text encoder	`gemma4-12b-with-proj-ltx-2.5-comfy-int8-convrot`	`gemma4-12b-with-proj-ltx-2.5-bf16`
steps	8	~24
guidance	`LTXVDualCFGGuider` at 1, 1	CFG ~4
sampler	`SamplerEulerAncestral` (eta 0, s_noise 1)	euler
sigmas	`ManualSigmas`, explicit 9-value list	`LTXVScheduler`

Verified working values

UNETLoader        ltx-2.5-22b-distilled-transformer-comfy-int8-convrot.safetensors, default
CLIPLoader        gemma4-12b-with-proj-ltx-2.5-comfy-int8-convrot.safetensors, type=ltxv
VAELoader         ltx-2.5-video-vae-bf16.safetensors        (video)
VAELoader         ltx-2.5-audio-vae-bf16.safetensors        (audio)
ManualSigmas      1.0, 0.99375, 0.9875, 0.98125, 0.975, 0.909375, 0.725, 0.421875, 0.0
SamplerEulerAncestral   eta 0, s_noise 1
LTXVDualCFGGuider       1, 1
LTXVAddGuide      frame_idx 0,  strength 0.7      (first frame)
LTXVAddGuide      frame_idx -1, strength 0.7      (last frame, chained off the first)
LTXVPreprocess    img_compression 18
size / length     1280 x 720, 5 s @ 24 fps
audio             LTXVEmptyLatentAudio — the model generates its own audio

Both guides run at strength 0.7, not 1.0, and the second consumes the first's conditioning and latent. LTXVCropGuides strips the guide frames before decode.

prompt_enhance

The preset ships it on, loading gemma4_e2b_it_bf16.safetensors as a second CLIP. It rewrites the prompt through Gemma before encoding.

Turn it off when the prompt contains dialogue you need spoken verbatim, or a trigger word. The rewriter will paraphrase both. It is also the documented reason a Comfy Cloud test destroyed the AKUSPACE trigger and the level words. Leave it on only for loose scene prompts where wording does not matter.

The AKUSPACE LoRA does not belong in this graph

Tested and confirmed on 2026-08-13: the adapter is reference-conditioned. It was trained to transform a reference audio input, so with no reference present it is off-distribution and produces near-silence at any strength. In a graph where audio is pinned by a zero noise mask it never runs at all.

The working chain is video render → take its generated audio → a2a pass with the LoRA → remux onto the same frames. That also gives the before/after pair for free: the untouched render is the base-model baseline.

Note loras/ltx-2.5-22b-distilled-lora-450-bf16.safetensors in the LTX repo is an unrelated distillation-acceleration LoRA, not ours.

Serving

ComfyUI on 8189 (8188 is a proxy on some templates). Reachable across a tailnet as http://<host>:8189. ComfyUI holds its weights in VRAM after a run — call POST /free {"unload_models":true,"free_memory":true} before running the trainer on the same GPU, or the a2a pass dies with CUDA OOM while Comfy sits on 66 GB.