From 2fac7a87263bd043feb56b1ff9a02e88cfae9479 Mon Sep 17 00:00:00 2001
From: Rattus <rattus128@gmail.com>
Date: Mon, 16 Mar 2026 19:20:39 +1000
Subject: [PATCH] wan: vae: encoder: Add feature cache layer that corks singles

If a downsample only gives you a single frame, save it to the feature
cache and return nothing to the top level. This increases the
efficiency of cacheability, but also prepares support for going two
by two rather than four by four on the frames.
---
 comfy/ldm/wan/vae.py | 39 +++++++++++++++++++++++++++------------
 1 file changed, 27 insertions(+), 12 deletions(-)

diff --git a/comfy/ldm/wan/vae.py b/comfy/ldm/wan/vae.py
index 71f73c64e..5b62cf123 100644
--- a/comfy/ldm/wan/vae.py
+++ b/comfy/ldm/wan/vae.py
@@ -99,7 +99,7 @@ class Resample(nn.Module):
         else:
             self.resample = nn.Identity()
 
-    def forward(self, x, feat_cache=None, feat_idx=[0]):
+    def forward(self, x, feat_cache=None, feat_idx=[0], final=False):
         b, c, t, h, w = x.size()
         if self.mode == 'upsample3d':
             if feat_cache is not None:
@@ -146,7 +146,6 @@ class Resample(nn.Module):
                 idx = feat_idx[0]
                 if feat_cache[idx] is None:
                     feat_cache[idx] = x.clone()
-                    feat_idx[0] += 1
                 else:
 
                     cache_x = x[:, :, -1:, :, :].clone()
@@ -157,7 +156,17 @@ class Resample(nn.Module):
                     x = self.time_conv(
                         torch.cat([feat_cache[idx][:, :, -1:, :, :], x], 2))
                     feat_cache[idx] = cache_x
-                    feat_idx[0] += 1
+
+                    deferred_x = feat_cache[idx + 1]
+                    if deferred_x is not None:
+                        x = torch.cat([deferred_x, x], 2)
+                        feat_cache[idx + 1] = None
+
+                    if x.shape[2] == 1 and not final:
+                        feat_cache[idx + 1] = x
+                        x = None
+
+                feat_idx[0] += 2
         return x
 
 
@@ -177,7 +186,7 @@ class ResidualBlock(nn.Module):
         self.shortcut = CausalConv3d(in_dim, out_dim, 1) \
             if in_dim != out_dim else nn.Identity()
 
-    def forward(self, x, feat_cache=None, feat_idx=[0]):
+    def forward(self, x, feat_cache=None, feat_idx=[0], final=False):
         old_x = x
         for layer in self.residual:
             if isinstance(layer, CausalConv3d) and feat_cache is not None:
@@ -213,7 +222,7 @@ class AttentionBlock(nn.Module):
         self.proj = ops.Conv2d(dim, dim, 1)
         self.optimized_attention = vae_attention()
 
-    def forward(self, x):
+    def forward(self, x, feat_cache=None, feat_idx=[0], final=False):
         identity = x
         b, c, t, h, w = x.size()
         x = rearrange(x, 'b c t h w -> (b t) c h w')
@@ -283,7 +292,7 @@ class Encoder3d(nn.Module):
             RMS_norm(out_dim, images=False), nn.SiLU(),
             CausalConv3d(out_dim, z_dim, 3, padding=1))
 
-    def forward(self, x, feat_cache=None, feat_idx=[0]):
+    def forward(self, x, feat_cache=None, feat_idx=[0], final=False):
         if feat_cache is not None:
             idx = feat_idx[0]
             cache_x = x[:, :, -CACHE_T:, :, :].clone()
@@ -303,7 +312,9 @@ class Encoder3d(nn.Module):
         ## downsamples
         for layer in self.downsamples:
             if feat_cache is not None:
-                x = layer(x, feat_cache, feat_idx)
+                x = layer(x, feat_cache, feat_idx, final=final)
+                if x is None:
+                    return None
             else:
                 x = layer(x)
 
@@ -441,10 +452,10 @@ class Decoder3d(nn.Module):
         return x
 
 
-def count_conv3d(model):
+def count_cache_layers(model):
     count = 0
     for m in model.modules():
-        if isinstance(m, CausalConv3d):
+        if isinstance(m, CausalConv3d) or (isinstance(m, Resample) and m.mode == 'downsample3d'):
             count += 1
     return count
 
@@ -485,7 +496,7 @@ class WanVAE(nn.Module):
         iter_ = 1 + (t - 1) // 4
         feat_map = None
         if iter_ > 1:
-            feat_map = [None] * count_conv3d(self.encoder)
+            feat_map = [None] * count_cache_layers(self.encoder)
         ## 对encode输入的x，按时间拆分为1、4、4、4....
         for i in range(iter_):
             conv_idx = [0]
@@ -498,8 +509,12 @@ class WanVAE(nn.Module):
                 out_ = self.encoder(
                     x[:, :, 1 + 4 * (i - 1):1 + 4 * i, :, :],
                     feat_cache=feat_map,
-                    feat_idx=conv_idx)
+                    feat_idx=conv_idx,
+                    final=(i == (iter_ - 1)))
+                if out_ is None:
+                    continue
                 out = torch.cat([out, out_], 2)
+
         mu, log_var = self.conv1(out).chunk(2, dim=1)
         return mu
 
@@ -509,7 +524,7 @@ class WanVAE(nn.Module):
         iter_ = z.shape[2]
         feat_map = None
         if iter_ > 1:
-            feat_map = [None] * count_conv3d(self.decoder)
+            feat_map = [None] * count_cache_layers(self.decoder)
         x = self.conv2(z)
         for i in range(iter_):
             conv_idx = [0]