Make time_embed_dim of UNet2DModel changeable

Author: Bichidian

src/diffusers/models/unets/unet_2d.py

@@ -97,6 +97,7 @@ def __init__(
         out_channels: int = 3,
         center_input_sample: bool = False,
         time_embedding_type: str = "positional",
+        time_embedding_dim: Optional[int] = None,
         freq_shift: int = 0,
         flip_sin_to_cos: bool = True,
         down_block_types: Tuple[str, ...] = ("DownBlock2D", "AttnDownBlock2D", "AttnDownBlock2D", "AttnDownBlock2D"),
@@ -122,7 +123,7 @@ def __init__(
         super().__init__()
 
         self.sample_size = sample_size
-        time_embed_dim = block_out_channels[0] * 4
+        time_embed_dim = time_embedding_dim or block_out_channels[0] * 4
 
         # Check inputs
         if len(down_block_types) != len(up_block_types):