LTX-2.5 SDR-to-HDR LoRA: ACEScg EXR and HLG, not an MP4 API

LTX-2.5 SDR-To-HDR is an open adapter that converts a standard-dynamic-range clip into HDR and writes scene-linear ACEScg EXR frames alongside an HLG master. It is a local pipeline, not an API. Sume's video routes return MP4 files, so if your finishing step needs EXR frames, this is a route Sume does not replace.

Facts below come from the SDR-To-HDR model card, read on 2026-10-02. The Sume side comes from Video generation and Video filter.

What does the SDR-To-HDR adapter take and return?

Per the card, the adapter expands highlight headroom and recovers range that an SDR grade compressed out. The SDR clip is itself the control signal. You can pass an SDR MP4 or MOV, or a directory of EXR frames, and choose the input colour space: sRGB gamma, sRGB, ACEScg or ACEScct. Outputs are ACEScg EXR frames and an HLG master.

• No text prompt: the card says it uses precomputed scene embeddings.
• Fixed at 8 distilled Euler steps.
• Frame count must be 8k+1.
• Needs the distilled transformer and video VAE from LTX-2.5, run through a dedicated hdr_ic_lora pipeline rather than the standard video-to-video one.
• ComfyUI is supported through the ComfyUI-LTXVideo extension.

Why does the EXR output matter?

EXR frames in scene-linear ACEScg are what a colour pipeline or compositing tool expects when it grades or merges plates. An 8-bit MP4 cannot carry that range. So the adapter sits at the end of a pipeline, after you have a finished SDR clip, and before the grade.

What can Sume do with the same clip?

A Sume video job completes with unsigned_urls pointing at a downloadable file, as the video docs describe. The docs do not describe HDR, EXR or a bit-depth option. Video filter is a pixel pass over one workspace clip that returns a new MP4 and does not describe a tone-mapping or colour-space conversion.

So the practical split is: generate or edit on Sume, download the MP4, then run SDR-To-HDR locally if you need HDR masters. Expect the adapter to invent highlight detail, because it is a generative model; it is not a lossless inverse of the grade. The card does not claim otherwise, and you should check the result against the intended look before delivery.

What does it cost to run yourself?

The card gives no price, and VRAM numbers are only described as 'sufficient' with memory limits for long or high-resolution content. Plan for your own GPU time and test one short clip first. The license is the LTX-2.x Community License, so read its terms for your company before you use outputs commercially.

Related reading on the Sume side: the earlier HDR and EXR export post explains why Sume stays MP4-only, and the frame count post explains the 8k+1 rule you hit here.