Add pretrained MAE weights, option to load checkpoints in ViT builder (…

…#479)

Summary:
For MAE fine-tuning, fine-tuning occurs just on the encoder (ViT). This change allows easy loading of MAE pretrained weights directly into our ViT class.

Pull Request resolved: #479

Test Plan:
```
python -m pytest -v tests/models/*
...
========== 207 passed, 25 warnings in 424.67s (0:07:04) ===========================

python -m pytest -v tests/modules/*
...
======================== 192 passed, 2 skipped, 22 warnings in 10.75s ==========================
```

Test instantiating ViT using MAE pretrained weights for each of the 3 checkpoints:

<img width="1163" alt="Screenshot 2023-10-05 at 6 39 02 PM" src="https://github.com/facebookresearch/multimodal/assets/24319399/c159b2dd-0b04-4572-85b9-d3024eee9a53">

Reviewed By: kartikayk

Differential Revision: D50015711

Pulled By: ebsmothers

fbshipit-source-id: e09fd02560b31574427b9f66373f12e7fd663f06

torchmultimodal/models/masked_auto_encoder/model.py

@@ -13,13 +13,25 @@
     get_2d_sin_cos_embeddings,
 )
 from torchmultimodal.models.masked_auto_encoder.swin_decoder import SwinTransformer
+from torchmultimodal.modules.encoders.vision_transformer import (
+    VisionTransformer,
+    vit_b_16,
+    vit_l_16,
+)
 from torchmultimodal.modules.layers.patch_embedding import PatchEmbeddings
 from torchmultimodal.modules.layers.transformer import (
     TransformerEncoder,
     TransformerOutput,
 )
 
 
+MAE_MODEL_MAPPING = {
+    "vit_b16_image": "https://download.pytorch.org/models/multimodal/mae/mae_pretrained_vit_base.pth",
+    "vit_l16_image": "https://download.pytorch.org/models/multimodal/mae/mae_pretrained_vit_large.pth",
+    "vit_b16_audio": "https://download.pytorch.org/models/multimodal/audio_mae/audio_mae_pretrained_vit_base.pth",
+}
+
+
 class MAEOutput(NamedTuple):
     encoder_output: Union[TransformerOutput, Tensor]
     decoder_pred: Optional[Tensor] = None
@@ -324,6 +336,16 @@ def vit_l_16_image_mae() -> MaskedAutoEncoder:
     )
 
 
+def vit_b_16_image_mae_encoder(pretrained: bool = False) -> VisionTransformer:
+    ckpt_path = MAE_MODEL_MAPPING["vit_b16_image"] if pretrained else None
+    return vit_b_16(final_layer_norm_eps=None, ckpt_path=ckpt_path)
+
+
+def vit_l_16_image_mae_encoder(pretrained: bool = False) -> VisionTransformer:
+    ckpt_path = MAE_MODEL_MAPPING["vit_l16_image"] if pretrained else None
+    return vit_l_16(final_layer_norm_eps=None, ckpt_path=ckpt_path)
+
+
 def audio_mae(
     *,
     # patch embedding
@@ -449,3 +471,13 @@ def vit_l_16_audio_mae() -> MaskedAutoEncoder:
         decoder_heads=16,
         decoder_dim_feedforward=2048,
     )
+
+
+def vit_b_16_audio_mae_encoder(pretrained: bool = False) -> VisionTransformer:
+    ckpt_path = MAE_MODEL_MAPPING["vit_b16_audio"] if pretrained else None
+    return vit_b_16(
+        final_layer_norm_eps=None,
+        num_channels=1,
+        image_size=(1024, 128),
+        ckpt_path=ckpt_path,
+    )

torchmultimodal/modules/encoders/vision_transformer.py

@@ -14,6 +14,7 @@
     TransformerEncoder,
     TransformerOutput,
 )
+from torchmultimodal.utils.common import load_module_from_url
 
 
 class VisionTransformer(nn.Module):
@@ -148,6 +149,7 @@ def vision_transformer(
     drop_path_rate: Optional[float] = None,
     patch_drop_rate: Optional[Union[float, Tuple[float, float]]] = None,
     pooler: Optional[nn.Module] = None,
+    ckpt_path: str = None,
 ) -> VisionTransformer:
     """
     Args:
@@ -198,6 +200,8 @@ def vision_transformer(
     vit = VisionTransformer(
         embeddings=image_embedding, encoder=transformer_encoder, pooler=pooler
     )
+    if ckpt_path:
+        load_module_from_url(vit, ckpt_path)
     return vit