feat: add LTX-2.5 support (#1893)

Co-authored-by: leejet <leejet714@gmail.com>

docs/ltx2.md

@@ -1,7 +1,17 @@
 # How to Use
 
+Both LTX-2.3 and LTX-2.5 are supported. The two share a transformer, video VAE and audio
+VAE architecture; LTX-2.5 drops the video FFN biases, adds a learned keyframe
+absolute-position embedding, and pairs with a Gemma 4 text encoder instead of Gemma 3.
+Everything is detected from the weights, so the command lines differ only in which files
+you pass.
+
+# LTX-2.3
+
 ## Download weights
 
+### LTX-2.3
+
 - Download LTX-2.3
     - safetensors: https://huggingface.co/Kijai/LTX2.3_comfy/tree/main/diffusion_models
     - gguf: https://huggingface.co/unsloth/LTX-2.3-GGUF/tree/main
@@ -16,6 +26,30 @@
 - Download LTX spatial latent upscaler
     - safetensors: https://huggingface.co/Lightricks/LTX-2.3/resolve/main/ltx-2.3-spatial-upscaler-x2-1.1.safetensors
 
+### LTX-2.5
+
+- Download LTX-2.5
+    - safetensors: https://huggingface.co/Lightricks/LTX-2.5/tree/main/diffusion_models
+    - gguf: https://huggingface.co/vantagewithai/LTX-2.5-GGUF/tree/main
+- Download the text encoder. This is a Gemma 4 12B fine-tuned for LTX with the text
+  projection bundled in, so no separate `--embeddings-connectors` file is needed. Google's
+  stock Gemma 4 is not a substitute.
+    - safetensors: https://huggingface.co/Lightricks/LTX-2.5/blob/main/text_encoders/gemma4-12b-with-proj-ltx-2.5-bf16.safetensors
+- Download the video vae. Use the **conv** variant: `ltx-2.5-video-vae-conv-bf16.safetensors`.
+  The default `ltx-2.5-video-vae-bf16.safetensors` is a diffusion decoder, which is not
+  implemented here.
+    - safetensors: https://huggingface.co/Lightricks/LTX-2.5/blob/main/vae/ltx-2.5-video-vae-conv-bf16.safetensors
+- Download the audio vae
+    - safetensors: https://huggingface.co/Lightricks/LTX-2.5/blob/main/vae/ltx-2.5-audio-vae-bf16.safetensors
+- Download the LTX spatial latent upscaler
+    - safetensors: https://huggingface.co/Lightricks/LTX-2.5/blob/main/latent_upscale_models/ltx-2.5-latent-spatial-upscaler-x2-bf16-1.0.safetensors
+
+To run the text encoder quantized, convert it once with sd-cli:
+
+```
+.\bin\Release\sd-cli.exe -M convert -m ..\models\text_encoders\gemma4-12b-with-proj-ltx-2.5-bf16.safetensors --type q8_0 -o ..\models\text_encoders\gemma4-12b-with-proj-ltx-2.5-Q8_0.gguf
+```
+
 ## Examples
 
 ### LTX-2.3 dev T2V
@@ -74,4 +108,32 @@ By default, the hires refine pass uses the main sampler and scheduler, then trim
   src="../assets/ltx2/hires_i2v.webm"
   controls
   muted
-  style="max-width: 100%; height: auto;"></video>
+  style="max-width: 100%; height: auto;"></video>
+
+### LTX-2.5 dev T2V
+
+```
+.\bin\Release\sd-cli.exe -M vid_gen --diffusion-model ..\models\diffusion_models\ltx-2.5-22b-dev-transformer-Q8_0.gguf --vae ..\models\vae\ltx-2.5-video-vae-conv-bf16.safetensors --audio-vae ..\models\vae\ltx-2.5-audio-vae-bf16.safetensors --llm ..\models\text_encoders\gemma4-12b-with-proj-ltx-2.5-Q8_0.gguf -p "A wide aerial shot of a red vintage convertible driving along a coastal cliff road at sunset, waves crashing below" --cfg-scale 3.0 --sampling-method euler -v -n "worst quality, low quality, blurry, distorted, artifacts" -W 1280 -H 720 --diffusion-fa --offload-to-cpu --video-frames 121 --fps 24 -o t2v.webm
+```
+
+### LTX-2.5 dev I2V
+
+```
+.\bin\Release\sd-cli.exe -M vid_gen --diffusion-model ..\models\diffusion_models\ltx-2.5-22b-dev-transformer-Q8_0.gguf --vae ..\models\vae\ltx-2.5-video-vae-conv-bf16.safetensors --audio-vae ..\models\vae\ltx-2.5-audio-vae-bf16.safetensors --llm ..\models\text_encoders\gemma4-12b-with-proj-ltx-2.5-Q8_0.gguf -p "a lovely cat blinking slowly, gentle camera push in" --cfg-scale 3.0 --sampling-method euler -v -W 1280 -H 720 --diffusion-fa --offload-to-cpu --video-frames 121 -i ..\assets\ernie_image\turbo_example.png -o i2v.webm
+```
+
+### LTX-2.5 spatial latent upscale
+
+Works exactly like the LTX-2.3 upscaler described below; put
+`ltx-2.5-latent-spatial-upscaler-x2-bf16-1.0.safetensors` under `--hires-upscalers-dir` and
+pass its name without path or extension to `--hires-upscaler`.
+
+```
+.\bin\Release\sd-cli.exe -M vid_gen --diffusion-model ..\models\diffusion_models\ltx-2.5-22b-dev-transformer-Q8_0.gguf --vae ..\models\vae\ltx-2.5-video-vae-conv-bf16.safetensors --audio-vae ..\models\vae\ltx-2.5-audio-vae-bf16.safetensors --llm ..\models\text_encoders\gemma4-12b-with-proj-ltx-2.5-Q8_0.gguf --hires-upscalers-dir ..\models\latent_upscale_models --hires-upscaler ltx-2.5-latent-spatial-upscaler-x2-bf16-1.0 --hires --hires-steps 6 -p "a lovely cat" --cfg-scale 3.0 --sampling-method euler -v -W 640 -H 360 --diffusion-fa --offload-to-cpu --video-frames 121 -o hires_t2v.webm
+```
+
+## Not implemented
+
+- The diffusion video decoder (`ltx-2.5-video-vae-bf16.safetensors`). Use the conv VAE.
+- The temporal latent upscaler and the duration head (`--auto-duration`); pass
+  `--video-frames` explicitly.