video_trunk.py

import inspect
import torch
import torch.nn as nn

from .video_stems import get_default_stem
from ._utils import Conv3DNoTemporal


BLOCK_CONFIG = {
    10: (1, 1, 1, 1),
    16: (2, 2, 2, 1),
    18: (2, 2, 2, 2),
    26: (2, 3, 4, 3),
    34: (3, 4, 6, 3),
    50: (3, 4, 6, 3),
    101: (3, 4, 23, 3),
    152: (3, 8, 36, 3)
}


class BasicBlock(nn.Module):

    expansion = 1

    def __init__(self, inplanes, planes, conv_builder, stride=1, downsample=None):
        midplanes = (inplanes * planes * 3 * 3 * 3) // (inplanes * 3 * 3 + 3 * planes)

        super(BasicBlock, self).__init__()
        self.conv1 = nn.Sequential(
            conv_builder(inplanes, planes, midplanes, stride),
            nn.BatchNorm3d(planes),
            nn.ReLU(inplace=True)
        )
        self.conv2 = nn.Sequential(
            conv_builder(planes, planes, midplanes),
            nn.BatchNorm3d(planes)
        )
        self.relu = nn.ReLU(inplace=True)
        self.downsample = downsample
        self.stride = stride

    def forward(self, x):
        residual = x

        out = self.conv1(x)
        out = self.conv2(out)
        if self.downsample is not None:
            residual = self.downsample(x)

        out += residual
        out = self.relu(out)

        return out


class Bottleneck(nn.Module):
    expansion = 4

    def __init__(self, inplanes, planes, conv_builder, stride=1, downsample=None):

        super(Bottleneck, self).__init__()
        midplanes = (inplanes * planes * 3 * 3 * 3) // (inplanes * 3 * 3 + 3 * planes)

        # 1x1x1
        self.conv1 = nn.Sequential(
            nn.Conv3d(inplanes, planes, kernel_size=1, bias=False),
            nn.BatchNorm3d(planes),
            nn.ReLU(inplace=True)
        )
        # Second kernel
        self.conv2 = nn.Sequential(
            conv_builder(planes, planes, midplanes, stride),
            nn.BatchNorm3d(planes),
            nn.ReLU(inplace=True)
        )

        # 1x1x1
        self.conv3 = nn.Sequential(
            nn.Conv3d(planes, planes * self.expansion, kernel_size=1, bias=False),
            nn.BatchNorm3d(planes * self.expansion)
        )
        self.relu = nn.ReLU(inplace=True)
        self.downsample = downsample
        self.stride = stride

    def forward(self, x):
        residual = x

        out = self.conv1(x)
        out = self.conv2(out)
        out = self.conv3(out)

        if self.downsample is not None:
            residual = self.downsample(x)

        out += residual
        out = self.relu(out)

        return out


class VideoTrunkBuilder(nn.Module):

    def __init__(self, block, conv_makers, model_depth,
                 stem=None,
                 num_classes=400,
                 zero_init_residual=False):
        """Generic resnet video generator.

        Args:
            block (nn.Module): resnet building block
            conv_makers (list(functions)): generator function for each layer
            model_depth (int): depth of the model; supports traditional resnet depths .
            stem (nn.Sequential, optional): Resnet stem, if None, defaults to conv-bn-relu. Defaults to None.
            num_classes (int, optional): Dimension of the final FC layer. Defaults to 400.
            zero_init_residual (bool, optional): Zero init bottleneck residual BN. Defaults to False.
        """
        super(VideoTrunkBuilder, self).__init__()
        layers = BLOCK_CONFIG[model_depth]
        self.inplanes = 64

        if stem is None:
            self.conv1 = get_default_stem()
        else:
            self.conv1 = stem

        self.layer1 = self._make_layer(block, conv_makers[0], 64, layers[0], stride=1)
        self.layer2 = self._make_layer(block, conv_makers[1], 128, layers[1], stride=2)
        self.layer3 = self._make_layer(block, conv_makers[2], 256, layers[2], stride=2)
        self.layer4 = self._make_layer(block, conv_makers[3], 512, layers[3], stride=2)

        self.avgpool = nn.AdaptiveAvgPool3d((1, 1, 1))
        self.fc = nn.Linear(512 * block.expansion, num_classes)

        # init weights
        self._initialize_weights()

        if zero_init_residual:
            for m in self.modules():
                if isinstance(m, Bottleneck):
                    nn.init.constant_(m.bn3.weight, 0)

    def forward(self, x):
        x = self.conv1(x)

        x = self.layer1(x)
        x = self.layer2(x)
        x = self.layer3(x)
        x = self.layer4(x)

        x = self.avgpool(x)
        # Flatten the layer to fc
        x = x.flatten(1)
        x = self.fc(x)

        return x

    def _make_layer(self, block, conv_builder, planes, blocks, stride=1):
        downsample = None

        if stride != 1 or self.inplanes != planes * block.expansion:
            ds_stride = conv_builder.get_downsample_stride(stride)
            downsample = nn.Sequential(
                nn.Conv3d(self.inplanes, planes * block.expansion,
                          kernel_size=1, stride=ds_stride, bias=False),
                nn.BatchNorm3d(planes * block.expansion)
            )
        layers = []
        layers.append(block(self.inplanes, planes, conv_builder, stride, downsample))

        self.inplanes = planes * block.expansion
        for i in range(1, blocks):
            layers.append(block(self.inplanes, planes, conv_builder))

        return nn.Sequential(*layers)

    def _initialize_weights(self):
        for m in self.modules():
            if isinstance(m, nn.Conv3d):
                nn.init.kaiming_normal_(m.weight, mode='fan_out',
                                        nonlinearity='relu')
                if m.bias is not None:
                    nn.init.constant_(m.bias, 0)
            elif isinstance(m, nn.BatchNorm3d):
                nn.init.constant_(m.weight, 1)
                nn.init.constant_(m.bias, 0)
            elif isinstance(m, nn.Linear):
                nn.init.normal_(m.weight, 0, 0.01)
                nn.init.constant_(m.bias, 0)