Before broadband was widely available, TiVo used to purchase overnight paid programming slots across the US and broadcast modified PDF417 video streams that provided weekly program guide data for TiVo users. There's a sample of it on YouTube https://www.youtube.com/watch?v=VfUgT2YoPzI but they usually wrapped a 60-second commercial before and after the 28-minute broadcast of data. There was enough error correction in the data streams to allow proper processing even with less-than-perfect analog television reception.