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diffusion_decoder differs from the current ltx-2.5-video-vae and lacks decoder.type_emb

#19
by christopher5106 - opened
Discussion
christopher5106

Hi! While porting the SDR-To-HDR IC-LoRA (with seam keyframes) to diffusers, we compared this repo's diffusion_decoder with the original Lightricks/LTX-2.5 vae/ltx-2.5-video-vae-bf16.safetensors. The two don't match:

  • Missing tag: the original file has the keyframe tag decoder.type_emb (BF16, [128]), and this repo's decoder does not.
  • Different weights: none of the 161 decoder tensors that can be matched by name are equal. The relative differences range from 2–6% on conv_in/conv_out to 10–40% on w_down, context_proj and upsamples.*. The latent statistics are identical.

On a decoder-only check with identical inputs and noise against Lightricks' own decoder (49 frames, 480x736), this repo's decoder matches at 44.4 dB for a plain decode and 35.2 dB with keyframes. The original VAE converted to diffusers matches at 62.2 dB and 68.6 dB.

The diffusers converter is updated to carry decoder.type_emb and set decoder_keyframe_type_embedding=True in https://github.com/huggingface/diffusers/pull/14975. Would you consider re-converting diffusion_decoder from the current original VAE with it? Happy to share the comparison script.

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