modeling_ecapa.py

import math
import torch
import typing as tp
import torch.nn as nn
import torch.nn.functional as F
from transformers.utils import ModelOutput
from transformers.modeling_utils import PreTrainedModel
from transformers.modeling_outputs import SequenceClassifierOutput

from .helpers_ecapa import Fbank
from .configuration_ecapa import EcapaConfig


class InputNormalization(nn.Module):

    spk_dict_mean: tp.Dict[int, torch.Tensor]
    spk_dict_std: tp.Dict[int, torch.Tensor]
    spk_dict_count: tp.Dict[int, int]

    def __init__(
        self,
        mean_norm=True,
        std_norm=True,
        norm_type="global",
        avg_factor=None,
        requires_grad=False,
        update_until_epoch=3,
    ):
        super().__init__()
        self.mean_norm = mean_norm
        self.std_norm = std_norm
        self.norm_type = norm_type
        self.avg_factor = avg_factor
        self.requires_grad = requires_grad
        self.glob_mean = torch.tensor([0])
        self.glob_std = torch.tensor([0])
        self.spk_dict_mean = {}
        self.spk_dict_std = {}
        self.spk_dict_count = {}
        self.weight = 1.0
        self.count = 0
        self.eps = 1e-10
        self.update_until_epoch = update_until_epoch

    def forward(self, input_values, lengths=None, spk_ids=torch.tensor([]), epoch=0):
        """Returns the tensor with the surrounding context.

        Arguments
        ---------
        x : tensor
            A batch of tensors.
        lengths : tensor
            A batch of tensors containing the relative length of each
            sentence (e.g, [0.7, 0.9, 1.0]). It is used to avoid
            computing stats on zero-padded steps.
        spk_ids : tensor containing the ids of each speaker (e.g, [0 10 6]).
            It is used to perform per-speaker normalization when
            norm_type='speaker'.
        """
        x = input_values
        N_batches = x.shape[0]

        current_means = []
        current_stds = []

        for snt_id in range(N_batches):
            # Avoiding padded time steps
            # lengths = torch.sum(attention_mask, dim=1)
            # relative_lengths = lengths / torch.max(lengths)
            # actual_size = torch.round(relative_lengths[snt_id] * x.shape[1]).int()
            actual_size = torch.round(lengths[snt_id] * x.shape[1]).int()

            # computing statistics
            current_mean, current_std = self._compute_current_stats(
                x[snt_id, 0:actual_size, ...]
            )

            current_means.append(current_mean)
            current_stds.append(current_std)

            if self.norm_type == "sentence":
                x[snt_id] = (x[snt_id] - current_mean.data) / current_std.data

            if self.norm_type == "speaker":
                spk_id = int(spk_ids[snt_id][0])

                if self.training:
                    if spk_id not in self.spk_dict_mean:
                        # Initialization of the dictionary
                        self.spk_dict_mean[spk_id] = current_mean
                        self.spk_dict_std[spk_id] = current_std
                        self.spk_dict_count[spk_id] = 1

                    else:
                        self.spk_dict_count[spk_id] = (
                            self.spk_dict_count[spk_id] + 1
                        )

                        if self.avg_factor is None:
                            self.weight = 1 / self.spk_dict_count[spk_id]
                        else:
                            self.weight = self.avg_factor

                        self.spk_dict_mean[spk_id] = (
                            (1 - self.weight) * self.spk_dict_mean[spk_id]
                            + self.weight * current_mean
                        )
                        self.spk_dict_std[spk_id] = (
                            (1 - self.weight) * self.spk_dict_std[spk_id]
                            + self.weight * current_std
                        )

                        self.spk_dict_mean[spk_id].detach()
                        self.spk_dict_std[spk_id].detach()

                    speaker_mean = self.spk_dict_mean[spk_id].data
                    speaker_std = self.spk_dict_std[spk_id].data
                else:
                    if spk_id in self.spk_dict_mean:
                        speaker_mean = self.spk_dict_mean[spk_id].data
                        speaker_std = self.spk_dict_std[spk_id].data
                    else:
                        speaker_mean = current_mean.data
                        speaker_std = current_std.data

                x[snt_id] = (x[snt_id] - speaker_mean) / speaker_std

        if self.norm_type == "batch" or self.norm_type == "global":
            current_mean = torch.mean(torch.stack(current_means), dim=0)
            current_std = torch.mean(torch.stack(current_stds), dim=0)

            if self.norm_type == "batch":
                x = (x - current_mean.data) / (current_std.data)

            if self.norm_type == "global":
                if self.training:
                    if self.count == 0:
                        self.glob_mean = current_mean
                        self.glob_std = current_std

                    elif epoch < self.update_until_epoch:
                        if self.avg_factor is None:
                            self.weight = 1 / (self.count + 1)
                        else:
                            self.weight = self.avg_factor

                        self.glob_mean = (
                            1 - self.weight
                        ) * self.glob_mean + self.weight * current_mean

                        self.glob_std = (
                            1 - self.weight
                        ) * self.glob_std + self.weight * current_std

                    self.glob_mean.detach()
                    self.glob_std.detach()

                    self.count = self.count + 1

                x = (x - self.glob_mean.data) / (self.glob_std.data)

        return x

    def _compute_current_stats(self, x):
        """Returns the tensor with the surrounding context.

        Arguments
        ---------
        x : tensor
            A batch of tensors.
        """
        # Compute current mean
        if self.mean_norm:
            current_mean = torch.mean(x, dim=0).detach().data
        else:
            current_mean = torch.tensor([0.0], device=x.device)

        # Compute current std
        if self.std_norm:
            current_std = torch.std(x, dim=0).detach().data
        else:
            current_std = torch.tensor([1.0], device=x.device)

        # Improving numerical stability of std
        current_std = torch.max(
            current_std, self.eps * torch.ones_like(current_std)
        )

        return current_mean, current_std

    def _statistics_dict(self):
        """Fills the dictionary containing the normalization statistics."""
        state = {}
        state["count"] = self.count
        state["glob_mean"] = self.glob_mean
        state["glob_std"] = self.glob_std
        state["spk_dict_mean"] = self.spk_dict_mean
        state["spk_dict_std"] = self.spk_dict_std
        state["spk_dict_count"] = self.spk_dict_count

        return state

    def _load_statistics_dict(self, state):
        """Loads the dictionary containing the statistics.

        Arguments
        ---------
        state : dict
            A dictionary containing the normalization statistics.
        """
        self.count = state["count"]
        if isinstance(state["glob_mean"], int):
            self.glob_mean = state["glob_mean"]
            self.glob_std = state["glob_std"]
        else:
            self.glob_mean = state["glob_mean"]  # .to(self.device_inp)
            self.glob_std = state["glob_std"]  # .to(self.device_inp)

        # Loading the spk_dict_mean in the right device
        self.spk_dict_mean = {}
        for spk in state["spk_dict_mean"]:
            self.spk_dict_mean[spk] = state["spk_dict_mean"][spk].to(
                self.device_inp
            )

        # Loading the spk_dict_std in the right device
        self.spk_dict_std = {}
        for spk in state["spk_dict_std"]:
            self.spk_dict_std[spk] = state["spk_dict_std"][spk].to(
                self.device_inp
            )

        self.spk_dict_count = state["spk_dict_count"]

        return state

    def to(self, device):
        """Puts the needed tensors in the right device."""
        self = super(InputNormalization, self).to(device)
        self.glob_mean = self.glob_mean.to(device)
        self.glob_std = self.glob_std.to(device)
        for spk in self.spk_dict_mean:
            self.spk_dict_mean[spk] = self.spk_dict_mean[spk].to(device)
            self.spk_dict_std[spk] = self.spk_dict_std[spk].to(device)
        return self


class TdnnLayer(nn.Module):

    def __init__(
        self, 
        in_channels, 
        out_channels, 
        kernel_size, 
        dilation=1, 
        stride=1, 
        groups=1, 
        padding=0, 
        padding_mode="reflect", 
        activation=torch.nn.LeakyReLU, 
    ):
        super(TdnnLayer, self).__init__()
        self.in_channels = in_channels
        self.out_channels = out_channels
        self.kernel_size = kernel_size
        self.dilation = dilation
        self.stride = stride
        self.groups = groups
        self.padding = padding
        self.padding_mode = padding_mode
        self.activation = activation()

        self.conv = nn.Conv1d(
            self.in_channels, 
            self.out_channels, 
            self.kernel_size, 
            dilation=self.dilation, 
            padding=self.padding, 
            groups=self.groups
        )

        # Set Affine=false to be compatible with the original kaldi version
        # self.ln = nn.LayerNorm(out_channels, elementwise_affine=False)
        self.norm = nn.BatchNorm1d(out_channels, affine=False)

    def forward(self, x):
        x = self._manage_padding(x, self.kernel_size, self.dilation, self.stride)
        out = self.conv(x)
        out = self.activation(out) 
        out = self.norm(out)
        return out

    def _manage_padding(
        self, x, kernel_size: int, dilation: int, stride: int,
    ):
        # Detecting input shape
        L_in = self.in_channels

        # Time padding
        padding = get_padding_elem(L_in, stride, kernel_size, dilation)

        # Applying padding
        x = F.pad(x, padding, mode=self.padding_mode)

        return x


def get_padding_elem(L_in: int, stride: int, kernel_size: int, dilation: int):
    """This function computes the number of elements to add for zero-padding.

    Arguments
    ---------
    L_in : int
    stride: int
    kernel_size : int
    dilation : int
    """
    if stride > 1:
        padding = [math.floor(kernel_size / 2), math.floor(kernel_size / 2)]

    else:
        L_out = (
            math.floor((L_in - dilation * (kernel_size - 1) - 1) / stride) + 1
        )
        padding = [
            math.floor((L_in - L_out) / 2),
            math.floor((L_in - L_out) / 2),
        ]
    return padding


class Res2NetBlock(torch.nn.Module):
    """An implementation of Res2NetBlock w/ dilation.

    Arguments
    ---------
    in_channels : int
        The number of channels expected in the input.
    out_channels : int
        The number of output channels.
    scale : int
        The scale of the Res2Net block.
    kernel_size: int
        The kernel size of the Res2Net block.
    dilation : int
        The dilation of the Res2Net block.

    Example
    -------
    >>> inp_tensor = torch.rand([8, 120, 64]).transpose(1, 2)
    >>> layer = Res2NetBlock(64, 64, scale=4, dilation=3)
    >>> out_tensor = layer(inp_tensor).transpose(1, 2)
    >>> out_tensor.shape
    torch.Size([8, 120, 64])
    """

    def __init__(
        self, in_channels, out_channels, scale=8, kernel_size=3, dilation=1
    ):
        super(Res2NetBlock, self).__init__()
        assert in_channels % scale == 0
        assert out_channels % scale == 0

        in_channel = in_channels // scale
        hidden_channel = out_channels // scale

        self.blocks = nn.ModuleList(
            [
                TdnnLayer(
                    in_channel,
                    hidden_channel,
                    kernel_size=kernel_size,
                    dilation=dilation,
                )
                for _ in range(scale - 1)
            ]
        )
        self.scale = scale

    def forward(self, x):
        """Processes the input tensor x and returns an output tensor."""
        y = []
        for i, x_i in enumerate(torch.chunk(x, self.scale, dim=1)):
            if i == 0:
                y_i = x_i
            elif i == 1:
                y_i = self.blocks[i - 1](x_i)
            else:
                y_i = self.blocks[i - 1](x_i + y_i)
            y.append(y_i)
        y = torch.cat(y, dim=1)
        return y


class SEBlock(nn.Module):
    """An implementation of squeeze-and-excitation block.

    Arguments
    ---------
    in_channels : int
        The number of input channels.
    se_channels : int
        The number of output channels after squeeze.
    out_channels : int
        The number of output channels.

    Example
    -------
    >>> inp_tensor = torch.rand([8, 120, 64]).transpose(1, 2)
    >>> se_layer = SEBlock(64, 16, 64)
    >>> lengths = torch.rand((8,))
    >>> out_tensor = se_layer(inp_tensor, lengths).transpose(1, 2)
    >>> out_tensor.shape
    torch.Size([8, 120, 64])
    """

    def __init__(self, in_channels, se_channels, out_channels):
        super(SEBlock, self).__init__()

        self.conv1 = nn.Conv1d(
            in_channels=in_channels, out_channels=se_channels, kernel_size=1
        )
        self.relu = torch.nn.ReLU(inplace=True)
        self.conv2 = nn.Conv1d(
            in_channels=se_channels, out_channels=out_channels, kernel_size=1
        )
        self.sigmoid = torch.nn.Sigmoid()

    def forward(self, x, lengths=None):
        """Processes the input tensor x and returns an output tensor."""
        L = x.shape[-1]
        if lengths is not None:
            mask = length_to_mask(lengths * L, max_len=L, device=x.device)
            mask = mask.unsqueeze(1)
            total = mask.sum(dim=2, keepdim=True)
            s = (x * mask).sum(dim=2, keepdim=True) / total
        else:
            s = x.mean(dim=2, keepdim=True)

        s = self.relu(self.conv1(s))
        s = self.sigmoid(self.conv2(s))

        return s * x


def length_to_mask(length, max_len=None, dtype=None, device=None):
    """Creates a binary mask for each sequence.

    Reference: https://discuss.pytorch.org/t/how-to-generate-variable-length-mask/23397/3

    Arguments
    ---------
    length : torch.LongTensor
        Containing the length of each sequence in the batch. Must be 1D.
    max_len : int
        Max length for the mask, also the size of the second dimension.
    dtype : torch.dtype, default: None
        The dtype of the generated mask.
    device: torch.device, default: None
        The device to put the mask variable.

    Returns
    -------
    mask : tensor
        The binary mask.

    Example
    -------
    >>> length=torch.Tensor([1,2,3])
    >>> mask=length_to_mask(length)
    >>> mask
    tensor([[1., 0., 0.],
            [1., 1., 0.],
            [1., 1., 1.]])
    """
    assert len(length.shape) == 1

    if max_len is None:
        max_len = length.max().long().item()  # using arange to generate mask
    mask = torch.arange(
        max_len, device=length.device, dtype=length.dtype
    ).expand(len(length), max_len) < length.unsqueeze(1)

    if dtype is None:
        dtype = length.dtype

    if device is None:
        device = length.device

    mask = torch.as_tensor(mask, dtype=dtype, device=device)
    return mask


class AttentiveStatisticsPooling(nn.Module):
    """This class implements an attentive statistic pooling layer for each channel.
    It returns the concatenated mean and std of the input tensor.

    Arguments
    ---------
    channels: int
        The number of input channels.
    attention_channels: int
        The number of attention channels.

    Example
    -------
    >>> inp_tensor = torch.rand([8, 120, 64]).transpose(1, 2)
    >>> asp_layer = AttentiveStatisticsPooling(64)
    >>> lengths = torch.rand((8,))
    >>> out_tensor = asp_layer(inp_tensor, lengths).transpose(1, 2)
    >>> out_tensor.shape
    torch.Size([8, 1, 128])
    """

    def __init__(self, channels, attention_channels=128, global_context=True):
        super().__init__()

        self.eps = 1e-12
        self.global_context = global_context
        if global_context:
            self.tdnn = TdnnLayer(channels * 3, attention_channels, 1, 1)
        else:
            self.tdnn = TdnnLayer(channels, attention_channels, 1, 1)
        self.tanh = nn.Tanh()
        self.conv = nn.Conv1d(
            in_channels=attention_channels, out_channels=channels, kernel_size=1
        )

    def forward(self, x, lengths=None):
        """Calculates mean and std for a batch (input tensor).

        Arguments
        ---------
        x : torch.Tensor
            Tensor of shape [N, C, L].
        """
        L = x.shape[-1]

        def _compute_statistics(x, m, dim=2, eps=self.eps):
            mean = (m * x).sum(dim)
            std = torch.sqrt(
                (m * (x - mean.unsqueeze(dim)).pow(2)).sum(dim).clamp(eps)
            )
            return mean, std

        if lengths is None:
            lengths = torch.ones(x.shape[0], device=x.device)

        # Make binary mask of shape [N, 1, L]
        mask = length_to_mask(lengths * L, max_len=L, device=x.device)
        mask = mask.unsqueeze(1)

        # Expand the temporal context of the pooling layer by allowing the
        # self-attention to look at global properties of the utterance.
        if self.global_context:
            # torch.std is unstable for backward computation
            # https://github.com/pytorch/pytorch/issues/4320
            total = mask.sum(dim=2, keepdim=True).float()
            mean, std = _compute_statistics(x, mask / total)
            mean = mean.unsqueeze(2).repeat(1, 1, L)
            std = std.unsqueeze(2).repeat(1, 1, L)
            attn = torch.cat([x, mean, std], dim=1)
        else:
            attn = x

        # Apply layers
        attn = self.conv(self.tanh(self.tdnn(attn)))

        # Filter out zero-paddings
        attn = attn.masked_fill(mask == 0, float("-inf"))

        attn = F.softmax(attn, dim=2)
        mean, std = _compute_statistics(x, attn)
        # Append mean and std of the batch
        pooled_stats = torch.cat((mean, std), dim=1)
        pooled_stats = pooled_stats.unsqueeze(2)

        return pooled_stats



class SERes2NetBlock(nn.Module):
    """An implementation of building block in ECAPA-TDNN, i.e.,
    TDNN-Res2Net-TDNN-SEBlock.

    Arguments
    ----------
    out_channels: int
        The number of output channels.
    res2net_scale: int
        The scale of the Res2Net block.
    kernel_size: int
        The kernel size of the TDNN blocks.
    dilation: int
        The dilation of the Res2Net block.
    activation : torch class
        A class for constructing the activation layers.
    groups: int
    Number of blocked connections from input channels to output channels.

    Example
    -------
    >>> x = torch.rand(8, 120, 64).transpose(1, 2)
    >>> conv = SERes2NetBlock(64, 64, res2net_scale=4)
    >>> out = conv(x).transpose(1, 2)
    >>> out.shape
    torch.Size([8, 120, 64])
    """

    def __init__(
        self,
        in_channels,
        out_channels,
        res2net_scale=8,
        se_channels=128,
        kernel_size=1,
        dilation=1,
        activation=torch.nn.ReLU,
        groups=1,
    ):
        super().__init__()
        self.out_channels = out_channels
        self.tdnn1 = TdnnLayer(
            in_channels,
            out_channels,
            kernel_size=1,
            dilation=1,
            activation=activation,
            groups=groups,
        )
        self.res2net_block = Res2NetBlock(
            out_channels, out_channels, res2net_scale, kernel_size, dilation
        )
        self.tdnn2 = TdnnLayer(
            out_channels,
            out_channels,
            kernel_size=1,
            dilation=1,
            activation=activation,
            groups=groups,
        )
        self.se_block = SEBlock(out_channels, se_channels, out_channels)

        self.shortcut = None
        if in_channels != out_channels:
            self.shortcut = nn.Conv1d(
                in_channels=in_channels,
                out_channels=out_channels,
                kernel_size=1,
            )

    def forward(self, x, lengths=None):
        """Processes the input tensor x and returns an output tensor."""
        residual = x
        if self.shortcut:
            residual = self.shortcut(x)

        x = self.tdnn1(x)
        x = self.res2net_block(x)
        x = self.tdnn2(x)
        x = self.se_block(x, lengths)

        return x + residual


class EcapaEmbedder(nn.Module):

    def __init__(
        self, 
        in_channels=80, 
        hidden_size=192,
        activation=torch.nn.ReLU,
        channels=[512, 512, 512, 512, 1536],
        kernel_sizes=[5, 3, 3, 3, 1],
        dilations=[1, 2, 3, 4, 1],
        attention_channels=128,
        res2net_scale=8,
        se_channels=128,
        global_context=True,
        groups=[1, 1, 1, 1, 1], 
    ) -> None:
        super(EcapaEmbedder, self).__init__()
        self.channels = channels
        self.blocks = nn.ModuleList()

        # The initial TDNN layer
        self.blocks.append(
            TdnnLayer(
                in_channels,
                channels[0],
                kernel_sizes[0],
                dilations[0],
                activation=activation,
                groups=groups[0],
            )
        )

        # SE-Res2Net layers
        for i in range(1, len(channels) - 1):
            self.blocks.append(
                SERes2NetBlock(
                    channels[i - 1],
                    channels[i],
                    res2net_scale=res2net_scale,
                    se_channels=se_channels,
                    kernel_size=kernel_sizes[i],
                    dilation=dilations[i],
                    activation=activation,
                    groups=groups[i],
                )
            )

        # Multi-layer feature aggregation
        self.mfa = TdnnLayer(
            channels[-2] * (len(channels) - 2),
            channels[-1],
            kernel_sizes[-1],
            dilations[-1],
            activation=activation,
            groups=groups[-1],
        )

        # Attentive Statistical Pooling
        self.asp = AttentiveStatisticsPooling(
            channels[-1],
            attention_channels=attention_channels,
            global_context=global_context,
        )
        self.asp_bn = nn.BatchNorm1d(channels[-1] * 2)

        # Final linear transformation
        self.fc = nn.Conv1d(
            in_channels=channels[-1] * 2,
            out_channels=hidden_size,
            kernel_size=1,
        )

    def forward(self, input_values, lengths=None):
        # Minimize transpose for efficiency
        x = input_values.transpose(1, 2)
        # lengths = torch.sum(attention_mask, dim=1)
        # lengths = lengths / torch.max(lengths)

        xl = []
        for layer in self.blocks:
            try:
                x = layer(x, lengths)
            except TypeError:
                x = layer(x)
            xl.append(x)

        # Multi-layer feature aggregation
        x = torch.cat(xl[1:], dim=1)
        x = self.mfa(x)

        # Attentive Statistical Pooling
        x = self.asp(x, lengths)
        x = self.asp_bn(x)

        # Final linear transformation
        x = self.fc(x)

        pooler_output = x.transpose(1, 2)
        pooler_output = pooler_output.squeeze(1)
        return ModelOutput(
            # last_hidden_state=last_hidden_state, 
            pooler_output=pooler_output
        )


class CosineSimilarityHead(torch.nn.Module):
    """
    This class implements the cosine similarity on the top of features.
    """
    def __init__(
        self,
        in_channels, 
        lin_blocks=0,
        hidden_size=192,
        num_classes=1211,
    ):
        super().__init__()
        self.blocks = nn.ModuleList()

        for block_index in range(lin_blocks):
            self.blocks.extend(
                [
                    nn.BatchNorm1d(num_features=in_channels),
                    nn.Linear(in_features=in_channels, out_features=hidden_size),
                ]
            )
            in_channels = hidden_size

        # Final Layer
        self.weight = nn.Parameter(
            torch.FloatTensor(num_classes, in_channels)
        )
        nn.init.xavier_uniform_(self.weight)

    def forward(self, x):
        """Returns the output probabilities over speakers.

        Arguments
        ---------
        x : torch.Tensor
            Torch tensor.
        """
        for layer in self.blocks:
            x = layer(x)

        # Need to be normalized
        x = F.linear(F.normalize(x), F.normalize(self.weight))
        return x


class EcapaPreTrainedModel(PreTrainedModel):

    config_class = EcapaConfig
    base_model_prefix = "ecapa"
    main_input_name = "input_values"
    supports_gradient_checkpointing = True

    def _init_weights(self, module):
        """Initialize the weights"""
        if isinstance(module, nn.Linear):
            # Slightly different from the TF version which uses truncated_normal for initialization
            # cf https://github.com/pytorch/pytorch/pull/5617
            module.weight.data.normal_(mean=0.0, std=self.config.initializer_range)
        elif isinstance(module, (nn.LayerNorm, nn.GroupNorm)):
            module.bias.data.zero_()
            module.weight.data.fill_(1.0)
        elif isinstance(module, nn.Conv1d):
            nn.init.kaiming_normal_(module.weight.data)

        if isinstance(module, (nn.Linear, nn.Conv1d)) and module.bias is not None:
            module.bias.data.zero_()


class EcapaModel(EcapaPreTrainedModel):

    def __init__(self, config):
        super().__init__(config)
        self.compute_features = Fbank(
            n_mels=config.n_mels, 
            sample_rate=config.sample_rate, 
            win_length=config.win_length, 
            hop_length=config.hop_length, 
        )
        self.mean_var_norm = InputNormalization(
            mean_norm=config.mean_norm, 
            std_norm=config.std_norm, 
            norm_type=config.norm_type
        )
        self.embedding_model = EcapaEmbedder(
            in_channels=config.n_mels, 
            channels=config.channels,
            kernel_sizes=config.kernel_sizes,
            dilations=config.dilations,
            attention_channels=config.attention_channels,
            res2net_scale=config.res2net_scale,
            se_channels=config.se_channels,
            global_context=config.global_context,
            groups=config.groups, 
            hidden_size=config.hidden_size
        )

    def forward(self, input_values, lengths=None):
        x = input_values
        # if attention_mask is None:
        #     attention_mask = torch.ones_like(input_values, device=x.device)
        x = self.compute_features(x)
        x = self.mean_var_norm(x, lengths)
        output = self.embedding_model(x, lengths)
        return ModelOutput(
            pooler_output=output.pooler_output, 
        )