Source code for espnet2.layers.time_warp

"""Time warp module."""

import torch

from espnet.nets.pytorch_backend.nets_utils import pad_list

DEFAULT_TIME_WARP_MODE = "bicubic"


def time_warp(x: torch.Tensor, window: int = 80, mode: str = DEFAULT_TIME_WARP_MODE):
    """Time warping using torch.interpolate.

    Args:
        x: (Batch, Time, Freq)
        window: time warp parameter
        mode: Interpolate mode
    """

    # bicubic supports 4D or more dimension tensor
    org_size = x.size()
    if x.dim() == 3:
        # x: (Batch, Time, Freq) -> (Batch, 1, Time, Freq)
        x = x[:, None]

    t = x.shape[2]
    if t - window <= window:
        return x.view(*org_size)

    center = torch.randint(window, t - window, (1,))[0]
    warped = torch.randint(center - window, center + window, (1,))[0] + 1

    # left: (Batch, Channel, warped, Freq)
    # right: (Batch, Channel, time - warped, Freq)
    left = torch.nn.functional.interpolate(
        x[:, :, :center], (warped, x.shape[3]), mode=mode, align_corners=False
    )
    right = torch.nn.functional.interpolate(
        x[:, :, center:], (t - warped, x.shape[3]), mode=mode, align_corners=False
    )

    if x.requires_grad:
        x = torch.cat([left, right], dim=-2)
    else:
        x[:, :, :warped] = left
        x[:, :, warped:] = right

    return x.view(*org_size)


class TimeWarp(torch.nn.Module):
    """Time warping using torch.interpolate.

    Args:
        window: time warp parameter
        mode: Interpolate mode
    """

    def __init__(self, window: int = 80, mode: str = DEFAULT_TIME_WARP_MODE):
        super().__init__()
        self.window = window
        self.mode = mode

    def extra_repr(self):
        return f"window={self.window}, mode={self.mode}"

    def forward(self, x: torch.Tensor, x_lengths: torch.Tensor = None):
        """Forward function.

        Args:
            x: (Batch, Time, Freq)
            x_lengths: (Batch,)
        """

        if x_lengths is None or all(le == x_lengths[0] for le in x_lengths):
            # Note that applying same warping for each sample
            y = time_warp(x, window=self.window, mode=self.mode)
        else:
            # FIXME(kamo): I have no idea to batchify Timewarp
            ys = []
            for i in range(x.size(0)):
                _y = time_warp(
                    x[i][None, : x_lengths[i]],
                    window=self.window,
                    mode=self.mode,
                )[0]
                ys.append(_y)
            y = pad_list(ys, 0.0)

        return y, x_lengths