- Attention: on sm_100+ with flash_attn.cute installed and FASTVIDEO_FA4 unset, the PAN2 pipeline turns FA4 on
before its modules load. One B300, 241 frames: 288 s instead of 670 s with the SDPA fallback. FASTVIDEO_FA4=0
keeps the previous backend.
- First frame: an image_path is read as its stored pixels, without the EXIF orientation rotation, as the reference
sampler reads it (load_image gains exif_transpose=True). All 11 sign-off inputs, one EXIF-rotated, now reach the
VAE bit-identical to the reference.
- Wan2.2 VAE decode kernel: each process builds in a temporary directory of its own instead of a shared
rank<LOCAL_RANK> directory, and finished builds go through the loader's keyed cache, added by atomic rename.
Two processes building at once both succeed; a later one fetches the build in about 2 s.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
- fastvideo-kernel/wan22_vae_decode: the Wan2.2 (TI2V-5B) VAE decoder on sm_100a / sm_103a at 704x1248, built on
first use against fastvideo-kernel's CUTLASS submodule. It frees intermediates early and carries 4 latent frames
per pass: a 5 s video peaks at 20.3 GiB, down from 94.6 GiB in the kernel's first version, with the same output.
- WanVAEConfig.decode_kernel routes AutoencoderKLWan.decode through it where it applies (bf16 with fp32
accumulation, about 7x faster than the fp32 decode on a B300, PSNR 61-63 dB, SSIM 0.998 against it);
decode_kernel_parallel splits the decode over the sequence-parallel group (2, 4 or 8 GPUs) and broadcasts the
video, with the ranks agreeing on whether every one of them could build the kernel.
- PAN2's DiT runs fused Triton kernels for Q/K RMSNorm + RoPE and LayerNorm + modulation (pan2_fusions,
set_fused_kernels).
- PAN2PipelineConfig turns all three on (vae_decode_kernel, vae_decode_kernel_parallel, dit_fused_kernels).
- VideoGenerator copies a decoded RGB video's frames to the host once instead of once per frame.
- The PAN2 presets sample at guidance 2.5, the reference launcher's default since 2026-10-23.
