From fc584aaa226560ccdfe70c2bcfe9424af1adeb04 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jukka=20Sepp=C3=A4nen?=
 <40791699+kijai@users.noreply.github.com>
Date: Tue, 22 Sep 2026 04:56:39 +0300
Subject: [PATCH] Blend H3 VAE tiles against composited neighbours (#16436)

---
 comfy/ldm/minimax/vae.py | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/comfy/ldm/minimax/vae.py b/comfy/ldm/minimax/vae.py
index 36d9abb57..cc4c16de7 100644
--- a/comfy/ldm/minimax/vae.py
+++ b/comfy/ldm/minimax/vae.py
@@ -599,38 +599,39 @@ class MiniMaxH3VideoVAE(nn.Module):
         y_idx, y_len, y_overlap = self.split_tiles(height)
         x_idx, x_len, x_overlap = self.split_tiles(width)
 
-        # Blended tiles are written straight into a pre-allocated canvas.
+        # Blended tiles are written straight into a pre-allocated canvas. Tiles blend against
+        # their neighbours as already blended, so seams stay continuous where overlaps cross.
         canvas = None
-        row_tails = []
+        strip = None
         out_y = 0
         for i, (i_pos, i_len) in enumerate(zip(y_idx, y_len)):
             zi, zl = i_pos // self.vae_ratio, i_len // self.vae_ratio
             tiles = self._decode_tile_row(z[..., zi:zi + zl, :], x_idx, x_len)
-            new_tails = []
+            new_strip = None
             left_tail = None
             out_x = 0
             # enumerate would retain the previous tile while the next batch decodes.
             for j in range(len(x_idx)):
                 tile = next(tiles)
-                if i < len(y_idx) - 1:
-                    new_tails.append(tile[..., -y_overlap[i]:, :].clone())
-                next_left_tail = tile[..., :, -x_overlap[j]:].clone() if j < len(x_idx) - 1 else None
                 if i > 0:
-                    tile = self.blend(row_tails[j], tile, y_overlap[i - 1], dim=-2)
+                    tile = self.blend(strip[..., :, x_idx[j]:x_idx[j] + x_len[j]], tile, y_overlap[i - 1], dim=-2)
                 if j > 0:
                     tile = self.blend(left_tail, tile, x_overlap[j - 1], dim=-1)
-                left_tail = next_left_tail
-                if i < len(y_idx) - 1:
-                    tile = tile[..., :-y_overlap[i], :]
+                left_tail = tile[..., :, -x_overlap[j]:].clone() if j < len(x_idx) - 1 else None
                 if j < len(x_idx) - 1:
                     tile = tile[..., :, :-x_overlap[j]]
                 if canvas is None:
                     canvas = torch.empty(*tile.shape[:-2], height, width, dtype=tile.dtype, device=tile.device)
+                if i < len(y_idx) - 1:
+                    if new_strip is None:
+                        new_strip = torch.empty(*tile.shape[:-2], y_overlap[i], width, dtype=tile.dtype, device=tile.device)
+                    new_strip[..., :, out_x:out_x + tile.shape[-1]] = tile[..., -y_overlap[i]:, :]
+                    tile = tile[..., :-y_overlap[i], :]
                 canvas[..., out_y:out_y + tile.shape[-2], out_x:out_x + tile.shape[-1]].copy_(tile)
                 tile_height = tile.shape[-2]
                 out_x += tile.shape[-1]
                 del tile
-            row_tails = new_tails
+            strip = new_strip
             out_y += tile_height
         return canvas