Wow! One of those moments when you realize that someone is doing exactly what you have been doing. My hobby project was seriously called QRTX. And each data frame started with ###-- where # are padded frame numbers. Pretty much identical to this guys project. Thanks for that find, I'm chuckling.

Points of difference: I was using a leading metadata frame with filename and total number of frames etc, and the receiving device were ACK'ing frame decodes with its own QR codes. Still, wow.