Wan Pipeline scaling fix, type hint warning, multi generator fix (#11007)

* Wan Pipeline scaling fix, type hint warning, multi generator fix

* Apply suggestions from code review

Author: hlky

src/diffusers/pipelines/wan/pipeline_wan_i2v.py

@@ -109,14 +109,30 @@ def prompt_clean(text):
 
 
 def retrieve_latents(
-    encoder_output: torch.Tensor, generator: Optional[torch.Generator] = None, sample_mode: str = "sample"
+    encoder_output: torch.Tensor,
+    latents_mean: torch.Tensor,
+    latents_std: torch.Tensor,
+    generator: Optional[torch.Generator] = None,
+    sample_mode: str = "sample",
 ):
     if hasattr(encoder_output, "latent_dist") and sample_mode == "sample":
+        encoder_output.latent_dist.mean = (encoder_output.latent_dist.mean - latents_mean) * latents_std
+        encoder_output.latent_dist.logvar = torch.clamp(
+            (encoder_output.latent_dist.logvar - latents_mean) * latents_std, -30.0, 20.0
+        )
+        encoder_output.latent_dist.std = torch.exp(0.5 * encoder_output.latent_dist.logvar)
+        encoder_output.latent_dist.var = torch.exp(encoder_output.latent_dist.logvar)
         return encoder_output.latent_dist.sample(generator)
     elif hasattr(encoder_output, "latent_dist") and sample_mode == "argmax":
+        encoder_output.latent_dist.mean = (encoder_output.latent_dist.mean - latents_mean) * latents_std
+        encoder_output.latent_dist.logvar = torch.clamp(
+            (encoder_output.latent_dist.logvar - latents_mean) * latents_std, -30.0, 20.0
+        )
+        encoder_output.latent_dist.std = torch.exp(0.5 * encoder_output.latent_dist.logvar)
+        encoder_output.latent_dist.var = torch.exp(encoder_output.latent_dist.logvar)
         return encoder_output.latent_dist.mode()
     elif hasattr(encoder_output, "latents"):
-        return encoder_output.latents
+        return (encoder_output.latents - latents_mean) * latents_std
     else:
         raise AttributeError("Could not access latents of provided encoder_output")
 
@@ -385,13 +401,6 @@ def prepare_latents(
         )
         video_condition = video_condition.to(device=device, dtype=dtype)
 
-        if isinstance(generator, list):
-            latent_condition = [retrieve_latents(self.vae.encode(video_condition), g) for g in generator]
-            latents = latent_condition = torch.cat(latent_condition)
-        else:
-            latent_condition = retrieve_latents(self.vae.encode(video_condition), generator)
-            latent_condition = latent_condition.repeat(batch_size, 1, 1, 1, 1)
-
         latents_mean = (
             torch.tensor(self.vae.config.latents_mean)
             .view(1, self.vae.config.z_dim, 1, 1, 1)
@@ -401,7 +410,14 @@ def prepare_latents(
             latents.device, latents.dtype
         )
 
-        latent_condition = (latent_condition - latents_mean) * latents_std
+        if isinstance(generator, list):
+            latent_condition = [
+                retrieve_latents(self.vae.encode(video_condition), latents_mean, latents_std, g) for g in generator
+            ]
+            latent_condition = torch.cat(latent_condition)
+        else:
+            latent_condition = retrieve_latents(self.vae.encode(video_condition), latents_mean, latents_std, generator)
+            latent_condition = latent_condition.repeat(batch_size, 1, 1, 1, 1)
 
         mask_lat_size = torch.ones(batch_size, 1, num_frames, latent_height, latent_width)
         mask_lat_size[:, :, list(range(1, num_frames))] = 0