"Ones and Zeros (bars and spaces)"

Take a look at a barcode: each bar and each space can be either thick or thin - you can't simply say that a bar (black) is a '1' and a space (white) is a '0'!
It doesn't make sense - that's why I want to know what he really means by "the bitstream"

Unfortunately, it doesn't seem like Leo can be bothered to contribute this clarification. :-(