Problem saving video streaming on a file

[tucano]

I tried to save a wmv stream with vlc on a file to make comparisons between codecs: I clicked on the option to register the incoming stream, without transcoding at the receiver, but I found that the two files are different, because the program I used to compare the 2 files (codec comparison) says THAT THEY HAVE DIFFERENT WIDTH .How could it be possible???

without transcoding at the receiver the files must be the same dimension....or not???