feat: add Flux.2 VAE proj matrix for previews

[stduhpf]

Seems like the proj is harder to train for this new VAE, reminds me of SDXL.

[stduhpf]

Not working, let me look into it. I think the latents are patchified by 2x2 patches or something

Edit: fixed

[leejet]

Perhaps placing the logic in preview_latent_video could make the code cleaner.

[stduhpf]

@leejet is it good now or should I actually move the calls to unpatchify_latents and repatchify_latents to be contained within preview_latent_video?

[leejet]

I think the best approach is to move unpatchify_latents logic into preview_latent_video, which would eliminate the need to call repatchify_latents.

[stduhpf]

I think the best approach is to move unpatchify_latents logic into preview_latent_video, which would eliminate the need to call repatchify_latents.

I will look into that soon. Maybe there's a way to avoid allcoating a temp buffer too by doing so, that would be great

[wbruna]

Not really related to the PR, but: maybe move the proj matrix selection to a virtual VAE object member, to avoid the decision tree here?

[stduhpf]

Indeed, that would probably be cleaner. Maybe in a follow-up PR.