[feat] Add pytorchvideo encoder wrapper (#1156)

Summary:
Pull Request resolved: #1156

Add an encoder class that constructs
any pytorchvideo model from config,
and uses this model for its forward pass.

Can load pretrained or random init models,
based on config.

Test Plan:
Tested through unit tests on slowfast50 and mvit.

Will be tested end-to-end when datasets and transformers are available in mmf

```
(torchvideo) ryanjiang@learnfair5083:~/copy/mmf$ pytest tests/models/test_mmf_transformer.py
================================================== test session starts ==================================================
platform linux -- Python 3.7.11, pytest-6.2.5, py-1.10.0, pluggy-1.0.0
rootdir: /private/home/ryanjiang/copy/mmf
plugins: forked-1.3.0, timeout-1.4.2, hydra-core-1.1.1, xdist-2.4.0, dash-2.0.0
collected 15 items

tests/models/test_mmf_transformer.py ...............                                                              [100%]

(torchvideo) ryanjiang@learnfair5083:~/copy/mmf$ pytest tests/modules/test_encoders.py
================================================== test session starts ==================================================
platform linux -- Python 3.7.11, pytest-6.2.5, py-1.10.0, pluggy-1.0.0
rootdir: /private/home/ryanjiang/copy/mmf
plugins: forked-1.3.0, timeout-1.4.2, hydra-core-1.1.1, xdist-2.4.0, dash-2.0.0
collected 12 items

tests/modules/test_encoders.py ............                                                                       [100%]
```

Reviewed By: apsdehal

Differential Revision: D32631207

Pulled By: Ryan-Qiyu-Jiang

fbshipit-source-id: 6b549162f7ae9ccea162563e48ed910618a6da54

mmf/modules/encoders.py

@@ -1,10 +1,12 @@
 # Copyright (c) Facebook, Inc. and its affiliates.
+import importlib
+import logging
 import os
 import pickle
 import re
 from collections import OrderedDict
 from copy import deepcopy
-from dataclasses import dataclass
+from dataclasses import asdict, dataclass
 from enum import Enum
 from typing import Any
 
@@ -25,13 +27,15 @@
 from transformers.configuration_auto import AutoConfig
 from transformers.modeling_auto import AutoModel
 
-
 try:
     from detectron2.modeling import ShapeSpec, build_resnet_backbone
 except ImportError:
     pass
 
 
+logger = logging.getLogger()
+
+
 class Encoder(nn.Module):
     @dataclass
     class Config:
@@ -688,6 +692,89 @@ def forward(self, x: Tensor) -> Tensor:
         return out
 
 
+@registry.register_encoder("pytorchvideo")
+class PytorchVideoEncoder(Encoder):
+    """A thin wrapper around pytorchvideo models.
+    This class is responsible for integrating pytorchvideo models as encoders.
+    THis class attempts to construct a pytorchvideo model from torch hub.
+    If this fails for a random weight model, and pytorchvideo package is available,
+    build the model with random weights from pytorchvideo.models.
+
+    Config:
+        name (str):         Always 'pytorchvideo' Used for builder_encoder()
+        random_init (bool): Flag to load pretrained weights
+        model_name (str):   Name of the pytorchvideo model to use
+        drop_last_n_layers (int):
+            <=0 value for the number of layers to drop off the end
+        pooler_name (str):  Name of pooler used on model output
+
+    Raises:
+        ImportError:
+        The constructor raises an ImportError if pytorchvideo is not installed.
+    """
+
+    @dataclass
+    class Config(Encoder.Config):
+        name: str = "pytorchvideo"
+        random_init: bool = False
+        model_name: str = "slowfast_r50"
+        drop_last_n_layers: int = -1
+        pooler_name: str = "identity"
+
+    PYTORCHVIDEO_REPO = "facebookresearch/pytorchvideo:main"
+
+    def __init__(self, config: Config):
+        super().__init__()
+        config = OmegaConf.create({**asdict(self.Config()), **config})
+        if config.random_init:
+            params = dict(**OmegaConf.to_container(config))
+            params = {
+                k: v
+                for k, v in params.items()
+                if k not in PytorchVideoEncoder.Config().__dict__
+            }
+            try:
+                model = torch.hub.load(
+                    PytorchVideoEncoder.PYTORCHVIDEO_REPO,
+                    model=config.model_name,
+                    pretrained=False,
+                    **params,
+                )
+            except BaseException as err:
+                pytorchvideo_spec = importlib.util.find_spec("pytorchvideo")
+                if pytorchvideo_spec is None:
+                    raise err
+                import pytorchvideo.models.hub as hub
+
+                model_create_fn = getattr(hub, config.model_name)
+                model = model_create_fn(pretrained=False, **params)
+        else:
+            # load weights from TorchHub
+            model = torch.hub.load(
+                PytorchVideoEncoder.PYTORCHVIDEO_REPO,
+                model=config.model_name,
+                pretrained=True,
+            )
+        encoder_list = []
+        if config.drop_last_n_layers == 0:
+            encoder_list += [model]
+        else:
+            modules_list = list(model.children())
+            if len(modules_list) == 1:
+                modules_list = list(modules_list[0].children())
+            modules = modules_list[: config.drop_last_n_layers]
+            encoder_list += modules
+
+        pooler = registry.get_pool_class(config.pooler_name)()
+        encoder_list += [pooler]
+        self.encoder = nn.Sequential(*encoder_list)
+
+    def forward(self, *args, **kwargs):
+        # pass along input to model
+        # assumes caller obeys the dynamic model signature
+        return self.encoder(*args, **kwargs)
+
+
 @registry.register_encoder("r2plus1d_18")
 class R2Plus1D18VideoEncoder(PooledEncoder):
     """

tests/models/test_mmf_transformer.py

@@ -21,7 +21,9 @@
 from mmf.utils.configuration import Configuration
 from mmf.utils.env import setup_imports, teardown_imports
 from omegaconf import OmegaConf
-
+from tests.test_utils import (
+    skip_if_no_pytorchvideo,
+)
 
 BERT_VOCAB_SIZE = 30255
 ROBERTA_VOCAB_SIZE = 50265
@@ -444,6 +446,63 @@ def test_preprocessing_with_resnet_encoder(self):
         test_utils.compare_tensors(segment_ids["image"], torch.tensor([[0], [0]]))
         test_utils.compare_tensors(segment_ids["text"], torch.ones((2, 128)).long())
 
+    @skip_if_no_pytorchvideo
+    def test_preprocessing_with_mvit_encoder(self):
+        encoder_config = OmegaConf.create(
+            {
+                "name": "pytorchvideo",
+                "model_name": "mvit_base_32x3",
+                "random_init": True,
+                "drop_last_n_layers": 0,
+                "pooler_name": "cls",
+                "spatial_size": 224,
+                "temporal_size": 8,
+                "head": None,
+                "embed_dim_mul": [[1, 2.0], [3, 2.0], [14, 2.0]],
+                "atten_head_mul": [[1, 2.0], [3, 2.0], [14, 2.0]],
+                "pool_q_stride_size": [[1, 1, 2, 2], [3, 1, 2, 2], [14, 1, 2, 2]],
+                "pool_kv_stride_adaptive": [1, 8, 8],
+                "pool_kvq_kernel": [3, 3, 3],
+            }
+        )
+        self._image_modality_config = MMFTransformerModalityConfig(
+            type="image",
+            key="image",
+            embedding_dim=768,
+            position_dim=1,
+            segment_id=0,
+            encoder=encoder_config,
+        )
+        modalities_config = [self._image_modality_config, self._text_modality_config]
+        config = MMFTransformer.Config(modalities=modalities_config, num_labels=2)
+        mmft = build_model(config)
+
+        sample_list = SampleList()
+        sample_list.image = torch.rand((2, 3, 8, 224, 224))
+        sample_list.text = torch.randint(0, 512, (2, 128))
+
+        transformer_input = mmft.preprocess_sample(sample_list)
+        input_ids = transformer_input["input_ids"]
+        self.assertEqual(input_ids["image"].dim(), 3)
+        self.assertEqual(list(input_ids["image"].size()), [2, 1, 768])
+
+        self.assertEqual(input_ids["text"].dim(), 2)
+        self.assertEqual(list(input_ids["text"].size()), [2, 128])
+
+        position_ids = transformer_input["position_ids"]
+        test_utils.compare_tensors(position_ids["image"], torch.tensor([[0], [0]]))
+        test_utils.compare_tensors(
+            position_ids["text"], torch.arange(0, 128).unsqueeze(0).expand((2, 128))
+        )
+
+        masks = transformer_input["masks"]
+        test_utils.compare_tensors(masks["image"], torch.tensor([[1], [1]]))
+        test_utils.compare_tensors(masks["text"], torch.ones((2, 128)).long())
+
+        segment_ids = transformer_input["segment_ids"]
+        test_utils.compare_tensors(segment_ids["image"], torch.tensor([[0], [0]]))
+        test_utils.compare_tensors(segment_ids["text"], torch.ones((2, 128)).long())
+
     def test_tie_mlm_head_weight_to_encoder(self):
         self._text_modality_config = MMFTransformerModalityConfig(
             type="text",

tests/modules/test_encoders.py

@@ -6,7 +6,11 @@
 import torch
 from mmf.modules import encoders
 from omegaconf import OmegaConf
-from tests.test_utils import setup_proxy, skip_if_old_transformers
+from tests.test_utils import (
+    setup_proxy,
+    skip_if_old_transformers,
+    skip_if_no_pytorchvideo,
+)
 from torch import nn
 
 
@@ -102,3 +106,59 @@ def test_vit_encoder(self):
         x = torch.rand(32, 197, 768)
         output, _ = encoder(x)
         self.assertEqual(output.size(-1), config.out_dim)
+
+    @skip_if_no_pytorchvideo
+    def test_pytorchvideo_slowfast_r50_encoder(self):
+        # instantiate video encoder from pytorchvideo
+        # default model is slowfast_r50
+        config = OmegaConf.structured(encoders.PytorchVideoEncoder.Config())
+        encoder = encoders.PytorchVideoEncoder(config)
+        fast = torch.rand((1, 3, 32, 224, 224))
+        slow = torch.rand((1, 3, 8, 224, 224))
+        output = encoder([slow, fast])
+        # check output tensor is the expected feature dim size
+        # (bs, feature_dim)
+        self.assertEqual(output.size(1), 2304)
+
+    @skip_if_no_pytorchvideo
+    def test_mvit_encoder(self):
+        config = {
+            "name": "pytorchvideo",
+            "model_name": "mvit_base_32x3",
+            "random_init": True,
+            "drop_last_n_layers": 0,
+            "pooler_name": "cls",
+            "spatial_size": 224,
+            "temporal_size": 8,
+            "head": None,
+            "embed_dim_mul": [[1, 2.0], [3, 2.0], [14, 2.0]],
+            "atten_head_mul": [[1, 2.0], [3, 2.0], [14, 2.0]],
+            "pool_q_stride_size": [[1, 1, 2, 2], [3, 1, 2, 2], [14, 1, 2, 2]],
+            "pool_kv_stride_adaptive": [1, 8, 8],
+            "pool_kvq_kernel": [3, 3, 3],
+        }
+        # test bert cls pooler
+        encoder = encoders.PytorchVideoEncoder(OmegaConf.create(config))
+        x = torch.rand((1, 3, 8, 224, 224))
+        output = encoder(x)
+        # check output tensor is the expected feature dim size
+        # based on pooled attention configs
+        # for more details consult https://arxiv.org/pdf/2104.11227
+        # and https://github.com/facebookresearch/pytorchvideo/
+        # (bs, num_features, feature_dim)
+        self.assertEqual(output.shape, torch.Size([1, 768]))
+
+        # test avg pooler
+        encoder = encoders.PytorchVideoEncoder(
+            OmegaConf.create(dict(config, pooler_name="avg"))
+        )
+        output = encoder(x)
+        self.assertEqual(output.shape, torch.Size([1, 768]))
+
+        # test no pooling
+        encoder = encoders.PytorchVideoEncoder(
+            OmegaConf.create(dict(config, pooler_name="identity"))
+        )
+        output = encoder(x)
+        # (bs, num_features, feature_dim)
+        self.assertEqual(output.shape, torch.Size([1, 197, 768]))

tests/test_utils.py

@@ -102,6 +102,13 @@ def wrap(testfn, reason="Requires newer version of transformers"):
     return wrap
 
 
+def skip_if_no_pytorchvideo(testfn, reason="Requires pytorchvideo"):
+    import importlib
+
+    pytorchvideo_spec = importlib.util.find_spec("pytorchvideo")
+    return unittest.skipIf(pytorchvideo_spec is None, reason)(testfn)
+
+
 def compare_state_dicts(a, b):
     same = True
     same = same and (list(a.keys()) == list(b.keys()))