kluk123:

As I understand, it can be interpreted as a set of 64 pictures, of height=100 pixels, width=1 pixel in a grayscale.


No, PyTorch uses the NCHW memory format (channels-first), so your input would have 64 channels and a single pixel.



 kluk123:

This layer requires the size of the input data to be specified and the size of the output data as well.


That’s not the case and you would need to define e.g. the in_channels, out_channels, and kernel_size.



 kluk123:

How does the ConvTranspose2d fit the output into an arbitrary number of output channels?


Each output channels is created by a filter kernel, so you can define this number arbitrarily.
For a general overview of the conv / transposed conv arithmetic, have a look at this tutorial 24.