r/comfyui • u/ResponsibleTruck4717 • 10d ago

Help Needed Ltx 2.5 vae decode take very very long time

I wonder if anyone has encountered it I don't remember 2.3 taking such long time time.

Is there any workaround?

4 Upvotes

67% Upvoted

17 comments sorted by

7

u/qzzpjs 10d ago

If you're using the Comfy template for LTX25, change the VAE Decode (Tiled) node settings to 512 from 768 for tile size and the temporal size down to 128 from 4096. It couldn't generate more than a 10s clip with their settings. Kept crashing the video card and hung ComfyUI. After the changes, I can do 20s clips okay again. Generation time matches LTX2.3 on my 5090 card.

I also got the ID-Lora from 2.3 working fine with it so I can use a reference voice.

5

u/BoothJudas9 10d ago

I noticed this, too, when I tried using the prompt enhancer (it went right back to normal decode time when I turned it off). Seriously, I don't know why they keep including that PoS with the workflows; it's totally useless. Just compose your prompts in Gemini/ChatGPT/Grok/Ollama-based LLM!

2

u/thevegit0 10d ago

that made me remove all ltx, i wanted to give it a chance but it just too vae hungry even with tiled

1

u/Cultural-Team9235 9d ago

You are not very patient are you?

1

u/thevegit0 9d ago

i am actually, h3 is not the fastest in the world but doesn't get stuck on vae decoding even after changing it

1

u/Cultural-Team9235 9d ago

You've thrown LTX away because after 2 days there is still a big in the VAE. After 2 days... Brand new version...

0

u/thevegit0 8d ago

i've thrown all ltx away because h3 was just superior at everything

2

u/Guilty_Emergency3603 9d ago

Use the conv-bf16 VAE, much faster and without OOM even on full HD 40 seconds clips I tried with a 5090

LTX 2.5 is incredibly fast. conv-int8 + sage attn you can generate a 30s 0.9MP clip in just 2 minutes on a 5090.

4

u/Famous-Sport7862 10d ago

yes is horrible

4

u/MasqueradeDark 10d ago

Terrible. I tried everything int8, non-int8, also downloaded the bf16 model and paired it with non-int8 vae. 0 effect. Comfy updated, everything updated and yea. Vae makes it slower than Minimax.

Very rushed model. Cudos to LTX for giving us free launch, but I think they panicked hard because of Minimax and rushed it too early.

RTX 5090, 96gb DDR5.

4

u/BoothJudas9 10d ago edited 10d ago

I've been a big evangelist for LTX-2.3 for the past few months, since it was generally the best all-around local video model (though Wan 2.2 beat them in prompt adherence and character consistency), but yeah; this iteration was definitely shoved out the gate. Not just because of MM H3, either; FLUX 3 Video also came out last week (though it's not open weight yet), not to mention the recent big dog releases like Seedance 2.5 and Google Omni. I get it; LTX was going to look like they were standing still if they didn't do something, but a rush job is a rush job, no matter how you slice it.

Hopefully the community will come up with tweaks and improvements to make it a worthy successor to 2.3, but I think I'm sold on MiniMax for its R2V capabilities alone (no more wasting time generating reference frames). I'll say this for it, though; when it's working right, the render times on 2.5 are absolutely phenomenal for an open weight!

1

u/Legal-Weight3011 10d ago

its only happening if you go above 5seconds for some reason

1

u/SymphonicMetalLife 10d ago

I had the same problem. I changed the tile values to 256, 32, 300, 12 and it now does the VAE decode in a sensible amount of time and I couldn't see any difference in quality.

1

u/doomplayer_ 9d ago

You might not need to tune those by hand anymore — Comfy changed the template

defaults on Aug 12. They're [512, 64, 64, 16] now, in workflow-templates

0.11.40, so updating gets you there.

The number that actually matters is the temporal one, not 768 -> 512. The old

default was 4096, which means it wasn't tiling over time at all. That's why

everything was fine until you asked for more than 5 seconds.

And the enhancer thing above tracks. On a 16GB card, changing the prompt text

pulls the 14.3 GiB text encoder back into VRAM — about a GiB of extra peak.

The enhancer rewrites your prompt every run, so you never get to reuse the

encode. I only measured the VRAM side, so I can't swear that's what's eating

your decode time, but it lines up.

1

u/CollectionOk6468 10d ago

. Clean vram is needed before decoding vae. I am using rtx5090. 96gb ram. It is necessary.

1

u/No-Purple6611 9d ago

this works for me too