    def __init__(self, input_nc=1, ndf=64, n_layers=3, use_actnorm=False):
        """
        Construct a 3D PatchGAN discriminator

        Parameters:
            input_nc (int)  -- the number of channels in input volumes
            ndf (int)       -- the number of filters in the last conv layer
            n_layers (int)  -- the number of conv layers in the discriminator
            use_actnorm (bool) -- flag to use actnorm instead of batchnorm
        """
        super(NLayerDiscriminator3D, self).__init__()
        if not use_actnorm:
            norm_layer = nn.BatchNorm3d
        else:
            raise NotImplementedError("Not implemented.")
        if type(norm_layer) == functools.partial:
            use_bias = norm_layer.func != nn.BatchNorm3d
        else:
            use_bias = norm_layer != nn.BatchNorm3d

        kw = 3
        padw = 1
        sequence = [nn.Conv3d(input_nc, ndf, kernel_size=kw, stride=2, padding=padw), nn.LeakyReLU(0.2, True)]
        nf_mult = 1
        nf_mult_prev = 1
        for n in range(1, n_layers):  # gradually increase the number of filters
            nf_mult_prev = nf_mult
            nf_mult = min(2 ** n, 8)
            sequence += [
                nn.Conv3d(ndf * nf_mult_prev, ndf * nf_mult, kernel_size=(kw, kw, kw), stride=(2 if n==1 else 1,2,2), padding=padw, bias=use_bias),
                norm_layer(ndf * nf_mult),
                nn.LeakyReLU(0.2, True)
            ]

        nf_mult_prev = nf_mult
        nf_mult = min(2 ** n_layers, 8)
        sequence += [
            nn.Conv3d(ndf * nf_mult_prev, ndf * nf_mult, kernel_size=(kw, kw, kw), stride=1, padding=padw, bias=use_bias),
            norm_layer(ndf * nf_mult),
            nn.LeakyReLU(0.2, True)
        ]

        sequence += [nn.Conv3d(ndf * nf_mult, 1, kernel_size=kw, stride=1, padding=padw)]  # output 1 channel prediction map
        self.main = nn.Sequential(*sequence)
Construct a 3D PatchGAN discriminator

Parameters:
input_nc (int)  -- the number of channels in input volumes
ndf (int)       -- the number of filters in the last conv layer
n_layers (int)  -- the number of conv layers in the discriminator
use_actnorm (bool) -- flag to use actnorm instead of batchnorm
opensora/models/causalvideovae/model/losses/discriminator.py