Have you ever wondered what those silver rectangles on the side of film cassettes are? They're called Camera Auto Sensing (CAS) codes and they're part of DX encoding, an industry standard first announced by Kodak in March 1983.

While DX encoding might be common knowledge for some DPReview readers, others — particularly the younger crowd — might not know what DX encoding is, how it works and what it took to become an industry standard.

These exact questions and more are answered and explained by Azriel Knight of the YouTube channel This Old Camera. In the six minute video, the first in a new series he's calling This Old Camera Xtra, he explains how Kodak introduced DX encoding, the purpose of the individual rectangles and how it became an ANSI and I3A standard that nearly all of the photography industry adopted, even though certain companies were a little hesitant to adopt.

You can find more of Azriel's videos by subscribing to his YouTube channel or following him on Twitter and Instagram.