# Copyright 2024-2025 The Alibaba Wan Team Authors. All rights reserved.
import math
import torch
import torch.cuda.amp as amp
import torch.nn as nn
from diffusers.configuration_utils import ConfigMixin, register_to_config
from diffusers.models.modeling_utils import ModelMixin
from .attention import flash_attention
__all__ = ['WanModel']
def sinusoidal_embedding_1d(dim, position):
# preprocess
assert dim % 2 == 0
half = dim // 2
position = position.type(torch.float64)
# calculation
sinusoid = torch.outer(
position, torch.pow(10000, -torch.arange(half).to(position).div(half)))
x = torch.cat([torch.cos(sinusoid), torch.sin(sinusoid)], dim=1)
return x
@amp.autocast(enabled=False)
def rope_params(max_seq_len, dim, theta=10000):
assert dim % 2 == 0
freqs = torch.outer(
torch.arange(max_seq_len),
1.0 / torch.pow(theta,
torch.arange(0, dim, 2).to(torch.float64).div(dim)))
freqs = torch.polar(torch.ones_like(freqs), freqs)
return freqs
@amp.autocast(enabled=False)
def rope_apply(x, grid_sizes, freqs):
n, c = x.size(2), x.size(3) // 2
# split freqs
freqs = freqs.split([c - 2 * (c // 3), c // 3, c // 3], dim=1)
# loop over samples
output = []
for i, (f, h, w) in enumerate(grid_sizes.tolist()):
seq_len = f * h * w
# precompute multipliers
x_i = torch.view_as_complex(x[i, :seq_len].to(torch.float64).reshape(
seq_len, n, -1, 2))
freqs_i = torch.cat([
freqs[0][:f].view(f, 1, 1, -1).expand(f, h, w, -1),
freqs[1][:h].view(1, h, 1, -1).expand(f, h, w, -1),
freqs[2][:w].view(1, 1, w, -1).expand(f, h, w, -1)
],
dim=-1).reshape(seq_len, 1, -1)
# apply rotary embedding
x_i = torch.view_as_real(x_i * freqs_i).flatten(2)
x_i = torch.cat([x_i, x[i, seq_len:]])
# append to collection
output.append(x_i)
return torch.stack(output).float()
class WanRMSNorm(nn.Module):
def __init__(self, dim, eps=1e-5):
super().__init__()
self.dim = dim
self.eps = eps
self.weight = nn.Parameter(torch.ones(dim))
def forward(self, x):
r"""
Args:
x(Tensor): Shape [B, L, C]
"""
return self._norm(x.float()).type_as(x) * self.weight
def _norm(self, x):
return x * torch.rsqrt(x.pow(2).mean(dim=-1, keepdim=True) + self.eps)
class WanLayerNorm(nn.LayerNorm):
def __init__(self, dim, eps=1e-6, elementwise_affine=False):
super().__init__(dim, elementwise_affine=elementwise_affine, eps=eps)
def forward(self, x):
r"""
Args:
x(Tensor): Shape [B, L, C]
"""
return super().forward(x.float()).type_as(x)
class WanSelfAttention(nn.Module):
def __init__(self,
dim,
num_heads,
window_size=(-1, -1),
qk_norm=True,
eps=1e-6):
assert dim % num_heads == 0
super().__init__()
self.dim = dim
self.num_heads = num_heads
self.head_dim = dim // num_heads
self.window_size = window_size
self.qk_norm = qk_norm
self.eps = eps
# layers
self.q = nn.Linear(dim, dim)
self.k = nn.Linear(dim, dim)
self.v = nn.Linear(dim, dim)
self.o = nn.Linear(dim, dim)
self.norm_q = WanRMSNorm(dim, eps=eps) if qk_norm else nn.Identity()
self.norm_k = WanRMSNorm(dim, eps=eps) if qk_norm else nn.Identity()
def forward(self, x, seq_lens, grid_sizes, freqs):
r"""
Args:
x(Tensor): Shape [B, L, num_heads, C / num_heads]
seq_lens(Tensor): Shape [B]
grid_sizes(Tensor): Shape [B, 3], the second dimension contains (F, H, W)
freqs(Tensor): Rope freqs, shape [1024, C / num_heads / 2]
"""
b, s, n, d = *x.shape[:2], self.num_heads, self.head_dim
# query, key, value function
def qkv_fn(x):
q = self.norm_q(self.q(x)).view(b, s, n, d)
k = self.norm_k(self.k(x)).view(b, s, n, d)
v = self.v(x).view(b, s, n, d)
return q, k, v
q, k, v = qkv_fn(x)
x = flash_attention(
q=rope_apply(q, grid_sizes, freqs),
k=rope_apply(k, grid_sizes, freqs),
v=v,
k_lens=seq_lens,
window_size=self.window_size)
# output
x = x.flatten(2)
x = self.o(x)
return x
class WanT2VCrossAttention(WanSelfAttention):
def forward(self, x, context, context_lens):
r"""
Args:
x(Tensor): Shape [B, L1, C]
context(Tensor): Shape [B, L2, C]
context_lens(Tensor): Shape [B]
"""
b, n, d = x.size(0), self.num_heads, self.head_dim
# compute query, key, value
q = self.norm_q(self.q(x)).view(b, -1, n, d)
k = self.norm_k(self.k(context)).view(b, -1, n, d)
v = self.v(context).view(b, -1, n, d)
# compute attention
x = flash_attention(q, k, v, k_lens=context_lens)
# output
x = x.flatten(2)
x = self.o(x)
return x
class WanI2VCrossAttention(WanSelfAttention):
def __init__(self,
dim,
num_heads,
window_size=(-1, -1),
qk_norm=True,
eps=1e-6):
super().__init__(dim, num_heads, window_size, qk_norm, eps)
self.k_img = nn.Linear(dim, dim)
self.v_img = nn.Linear(dim, dim)
# self.alpha = nn.Parameter(torch.zeros((1, )))
self.norm_k_img = WanRMSNorm(dim, eps=eps) if qk_norm else nn.Identity()
def forward(self, x, context, context_lens):
r"""
Args:
x(Tensor): Shape [B, L1, C]
context(Tensor): Shape [B, L2, C]
context_lens(Tensor): Shape [B]
"""
context_img = context[:, :257]
context = context[:, 257:]
b, n, d = x.size(0), self.num_heads, self.head_dim
# compute query, key, value
q = self.norm_q(self.q(x)).view(b, -1, n, d)
k = self.norm_k(self.k(context)).view(b, -1, n, d)
v = self.v(context).view(b, -1, n, d)
k_img = self.norm_k_img(self.k_img(context_img)).view(b, -1, n, d)
v_img = self.v_img(context_img).view(b, -1, n, d)
img_x = flash_attention(q, k_img, v_img, k_lens=None)
# compute attention
x = flash_attention(q, k, v, k_lens=context_lens)
# output
x = x.flatten(2)
img_x = img_x.flatten(2)
x = x + img_x
x = self.o(x)
return x
WAN_CROSSATTENTION_CLASSES = {
't2v_cross_attn': WanT2VCrossAttention,
'i2v_cross_attn': WanI2VCrossAttention,
}
class WanAttentionBlock(nn.Module):
def __init__(self,
cross_attn_type,
dim,
ffn_dim,
num_heads,
window_size=(-1, -1),
qk_norm=True,
cross_attn_norm=False,
eps=1e-6):
super().__init__()
self.dim = dim
self.ffn_dim = ffn_dim
self.num_heads = num_heads
self.window_size = window_size
self.qk_norm = qk_norm
self.cross_attn_norm = cross_attn_norm
self.eps = eps
# layers
self.norm1 = WanLayerNorm(dim, eps)
self.self_attn = WanSelfAttention(dim, num_heads, window_size, qk_norm,
eps)
self.norm3 = WanLayerNorm(
dim, eps,
elementwise_affine=True) if cross_attn_norm else nn.Identity()
self.cross_attn = WAN_CROSSATTENTION_CLASSES[cross_attn_type](dim,
num_heads,
(-1, -1),
qk_norm,
eps)
self.norm2 = WanLayerNorm(dim, eps)
self.ffn = nn.Sequential(
nn.Linear(dim, ffn_dim), nn.GELU(approximate='tanh'),
nn.Linear(ffn_dim, dim))
# modulation
self.modulation = nn.Parameter(torch.randn(1, 6, dim) / dim**0.5)
def forward(
self,
x,
e,
seq_lens,
grid_sizes,
freqs,
context,
context_lens,
):
r"""
Args:
x(Tensor): Shape [B, L, C]
e(Tensor): Shape [B, 6, C]
seq_lens(Tensor): Shape [B], length of each sequence in batch
grid_sizes(Tensor): Shape [B, 3], the second dimension contains (F, H, W)
freqs(Tensor): Rope freqs, shape [1024, C / num_heads / 2]
"""
assert e.dtype == torch.float32
with amp.autocast(dtype=torch.float32):
e = (self.modulation + e).chunk(6, dim=1)
assert e[0].dtype == torch.float32
# self-attention
y = self.self_attn(
self.norm1(x).float() * (1 + e[1]) + e[0], seq_lens, grid_sizes,
freqs)
with amp.autocast(dtype=torch.float32):
x = x + y * e[2]
# cross-attention & ffn function
def cross_attn_ffn(x, context, context_lens, e):
x = x + self.cross_attn(self.norm3(x), context, context_lens)
y = self.ffn(self.norm2(x).float() * (1 + e[4]) + e[3])
with amp.autocast(dtype=torch.float32):
x = x + y * e[5]
return x
x = cross_attn_ffn(x, context, context_lens, e)
return x
class Head(nn.Module):
def __init__(self, dim, out_dim, patch_size, eps=1e-6):
super().__init__()
self.dim = dim
self.out_dim = out_dim
self.patch_size = patch_size
self.eps = eps
# layers
out_dim = math.prod(patch_size) * out_dim
self.norm = WanLayerNorm(dim, eps)
self.head = nn.Linear(dim, out_dim)
# modulation
self.modulation = nn.Parameter(torch.randn(1, 2, dim) / dim**0.5)
def forward(self, x, e):
r"""
Args:
x(Tensor): Shape [B, L1, C]
e(Tensor): Shape [B, C]
"""
assert e.dtype == torch.float32
with amp.autocast(dtype=torch.float32):
e = (self.modulation + e.unsqueeze(1)).chunk(2, dim=1)
x = (self.head(self.norm(x) * (1 + e[1]) + e[0]))
return x
class MLPProj(torch.nn.Module):
def __init__(self, in_dim, out_dim):
super().__init__()
self.proj = torch.nn.Sequential(
torch.nn.LayerNorm(in_dim), torch.nn.Linear(in_dim, in_dim),
torch.nn.GELU(), torch.nn.Linear(in_dim, out_dim),
torch.nn.LayerNorm(out_dim))
def forward(self, image_embeds):
clip_extra_context_tokens = self.proj(image_embeds)
return clip_extra_context_tokens
class WanModel(ModelMixin, ConfigMixin):
r"""
Wan diffusion backbone supporting both text-to-video and image-to-video.
"""
ignore_for_config = [
'patch_size', 'cross_attn_norm', 'qk_norm', 'text_dim', 'window_size'
]
_no_split_modules = ['WanAttentionBlock']
@register_to_config
def __init__(self,
model_type='t2v',
patch_size=(1, 2, 2),
text_len=512,
in_dim=16,
dim=2048,
ffn_dim=8192,
freq_dim=256,
text_dim=4096,
out_dim=16,
num_heads=16,
num_layers=32,
window_size=(-1, -1),
qk_norm=True,
cross_attn_norm=True,
eps=1e-6):
r"""
Initialize the diffusion model backbone.
Args:
model_type (`str`, *optional*, defaults to 't2v'):
Model variant - 't2v' (text-to-video) or 'i2v' (image-to-video)
patch_size (`tuple`, *optional*, defaults to (1, 2, 2)):
3D patch dimensions for video embedding (t_patch, h_patch, w_patch)
text_len (`int`, *optional*, defaults to 512):
Fixed length for text embeddings
in_dim (`int`, *optional*, defaults to 16):
Input video channels (C_in)
dim (`int`, *optional*, defaults to 2048):
Hidden dimension of the transformer
ffn_dim (`int`, *optional*, defaults to 8192):
Intermediate dimension in feed-forward network
freq_dim (`int`, *optional*, defaults to 256):
Dimension for sinusoidal time embeddings
text_dim (`int`, *optional*, defaults to 4096):
Input dimension for text embeddings
out_dim (`int`, *optional*, defaults to 16):
Output video channels (C_out)
num_heads (`int`, *optional*, defaults to 16):
Number of attention heads
num_layers (`int`, *optional*, defaults to 32):
Number of transformer blocks
window_size (`tuple`, *optional*, defaults to (-1, -1)):
Window size for local attention (-1 indicates global attention)
qk_norm (`bool`, *optional*, defaults to True):
Enable query/key normalization
cross_attn_norm (`bool`, *optional*, defaults to False):
Enable cross-attention normalization
eps (`float`, *optional*, defaults to 1e-6):
Epsilon value for normalization layers
"""
super().__init__()
assert model_type in ['t2v', 'i2v']
self.model_type = model_type
self.patch_size = patch_size
self.text_len = text_len
self.in_dim = in_dim
self.dim = dim
self.ffn_dim = ffn_dim
self.freq_dim = freq_dim
self.text_dim = text_dim
self.out_dim = out_dim
self.num_heads = num_heads
self.num_layers = num_layers
self.window_size = window_size
self.qk_norm = qk_norm
self.cross_attn_norm = cross_attn_norm
self.eps = eps
# embeddings
self.patch_embedding = nn.Conv3d(
in_dim, dim, kernel_size=patch_size, stride=patch_size)
self.text_embedding = nn.Sequential(
nn.Linear(text_dim, dim), nn.GELU(approximate='tanh'),
nn.Linear(dim, dim))
self.time_embedding = nn.Sequential(
nn.Linear(freq_dim, dim), nn.SiLU(), nn.Linear(dim, dim))
self.time_projection = nn.Sequential(nn.SiLU(), nn.Linear(dim, dim * 6))
# blocks
cross_attn_type = 't2v_cross_attn' if model_type == 't2v' else 'i2v_cross_attn'
self.blocks = nn.ModuleList([
WanAttentionBlock(cross_attn_type, dim, ffn_dim, num_heads,
window_size, qk_norm, cross_attn_norm, eps)
for _ in range(num_layers)
])
# head
self.head = Head(dim, out_dim, patch_size, eps)
# buffers (don't use register_buffer otherwise dtype will be changed in to())
assert (dim % num_heads) == 0 and (dim // num_heads) % 2 == 0
d = dim // num_heads
self.freqs = torch.cat([
rope_params(1024, d - 4 * (d // 6)),
rope_params(1024, 2 * (d // 6)),
rope_params(1024, 2 * (d // 6))
],
dim=1)
if model_type == 'i2v':
self.img_emb = MLPProj(1280, dim)
# initialize weights
self.init_weights()
def forward(
self,
x,
t,
context,
seq_len,
clip_fea=None,
y=None,
):
r"""
Forward pass through the diffusion model
Args:
x (List[Tensor]):
List of input video tensors, each with shape [C_in, F, H, W]
t (Tensor):
Diffusion timesteps tensor of shape [B]
context (List[Tensor]):
List of text embeddings each with shape [L, C]
seq_len (`int`):
Maximum sequence length for positional encoding
clip_fea (Tensor, *optional*):
CLIP image features for image-to-video mode
y (List[Tensor], *optional*):
Conditional video inputs for image-to-video mode, same shape as x
Returns:
List[Tensor]:
List of denoised video tensors with original input shapes [C_out, F, H / 8, W / 8]
"""
if self.model_type == 'i2v':
assert clip_fea is not None and y is not None
# params
device = self.patch_embedding.weight.device
if self.freqs.device != device:
self.freqs = self.freqs.to(device)
if y is not None:
x = [torch.cat([u, v], dim=0) for u, v in zip(x, y)]
# embeddings
x = [self.patch_embedding(u.unsqueeze(0)) for u in x]
grid_sizes = torch.stack(
[torch.tensor(u.shape[2:], dtype=torch.long) for u in x])
x = [u.flatten(2).transpose(1, 2) for u in x]
seq_lens = torch.tensor([u.size(1) for u in x], dtype=torch.long)
assert seq_lens.max() <= seq_len
x = torch.cat([
torch.cat([u, u.new_zeros(1, seq_len - u.size(1), u.size(2))],
dim=1) for u in x
])
# time embeddings
with amp.autocast(dtype=torch.float32):
e = self.time_embedding(
sinusoidal_embedding_1d(self.freq_dim, t).float())
e0 = self.time_projection(e).unflatten(1, (6, self.dim))
assert e.dtype == torch.float32 and e0.dtype == torch.float32
# context
context_lens = None
context = self.text_embedding(
torch.stack([
torch.cat(
[u, u.new_zeros(self.text_len - u.size(0), u.size(1))])
for u in context
]))
if clip_fea is not None:
context_clip = self.img_emb(clip_fea) # bs x 257 x dim
context = torch.concat([context_clip, context], dim=1)
# arguments
kwargs = dict(
e=e0,
seq_lens=seq_lens,
grid_sizes=grid_sizes,
freqs=self.freqs,
context=context,
context_lens=context_lens)
for block in self.blocks:
x = block(x, **kwargs)
# head
x = self.head(x, e)
# unpatchify
x = self.unpatchify(x, grid_sizes)
return [u.float() for u in x]
def unpatchify(self, x, grid_sizes):
r"""
Reconstruct video tensors from patch embeddings.
Args:
x (List[Tensor]):
List of patchified features, each with shape [L, C_out * prod(patch_size)]
grid_sizes (Tensor):
Original spatial-temporal grid dimensions before patching,
shape [B, 3] (3 dimensions correspond to F_patches, H_patches, W_patches)
Returns:
List[Tensor]:
Reconstructed video tensors with shape [C_out, F, H / 8, W / 8]
"""
c = self.out_dim
out = []
for u, v in zip(x, grid_sizes.tolist()):
u = u[:math.prod(v)].view(*v, *self.patch_size, c)
u = torch.einsum('fhwpqrc->cfphqwr', u)
u = u.reshape(c, *[i * j for i, j in zip(v, self.patch_size)])
out.append(u)
return out
def init_weights(self):
r"""
Initialize model parameters using Xavier initialization.
"""
# basic init
for m in self.modules():
if isinstance(m, nn.Linear):
nn.init.xavier_uniform_(m.weight)
if m.bias is not None:
nn.init.zeros_(m.bias)
# init embeddings
nn.init.xavier_uniform_(self.patch_embedding.weight.flatten(1))
for m in self.text_embedding.modules():
if isinstance(m, nn.Linear):
nn.init.normal_(m.weight, std=.02)
for m in self.time_embedding.modules():
if isinstance(m, nn.Linear):
nn.init.normal_(m.weight, std=.02)
# init output layer
nn.init.zeros_(self.head.head.weight)