Add CogVideoX diffusers-to-original format conversion script

[Ricardo-M-L]

Summary

• Adds scripts/convert_cogvideox_to_original.py, a reverse conversion script that converts CogVideoX models (transformer and VAE) from diffusers format back to the original CogVideo checkpoint format
• Reverses all weight name mappings, tensor concatenations (q/k/v merging), and adaln norm interleaving from the existing convert_cogvideox_to_diffusers.py
• Supports both transformer and VAE components with fp16/bf16 precision options

Closes #10076

How to use

# Convert transformer
python scripts/convert_cogvideox_to_original.py \
    --diffusers_model_path THUDM/CogVideoX-2b \
    --output_path ./cogvideox_original/transformer.pt \
    --component transformer

# Convert VAE
python scripts/convert_cogvideox_to_original.py \
    --diffusers_model_path THUDM/CogVideoX-2b \
    --output_path ./cogvideox_original/vae.pt \
    --component vae

# With fp16 precision
python scripts/convert_cogvideox_to_original.py \
    --diffusers_model_path THUDM/CogVideoX-5b \
    --output_path ./cogvideox_original/transformer.pt \
    --component transformer --fp16

Implementation details

The script reverses every transformation in convert_cogvideox_to_diffusers.py:

Forward (to diffusers)	Reverse (to original)
query_key_value chunked into to_q, to_k, to_v	to_q/k/v concatenated back into query_key_value
adaln_layer.adaLN_modulations split into norm1.linear + norm2.linear	norm1/norm2.linear interleaved back into adaLN_modulations
query/key_layernorm_list renamed to attn1.norm_q/k	attn1.norm_q/k renamed back to query/key_layernorm_list
All simple key renames via TRANSFORMER_KEYS_RENAME_DICT	Reversed via TRANSFORMER_KEYS_RENAME_DICT_REVERSE
VAE up_blocks index inversion	Re-inverted back to original indices
model.diffusion_model. prefix stripped	Prefix re-added

Test plan

• Verify round-trip: convert original -> diffusers -> original and compare state dict keys
• Test with CogVideoX-2B (30 layers, 30 heads)
• Test with CogVideoX-5B (42 layers, 48 heads)
• Test VAE conversion independently

🤖 Generated with Claude Code