As a more recent example of a similar concept, TiVo would distribute guide data to their DVRs using encoded video broadcast during overnight Paid Programming time slots. The practice ran from about 1999 to 2016. Around 2016, TiVo discontinued support for guide data updates for their first-generation Series1 DVRs. I couldn't find much information about these broadcasts online, though someone did post a clip of one from 2003 [1], there are a few copies of more recent introduction and conclusion animations [2], and there is some information about them on Wikipedia [3]. It could be a fun project to try to decode it.

[1]: https://www.youtube.com/watch?v=VfUgT2YoPzI

[2]: https://www.youtube.com/watch?v=Hnu97CHDrYI

[3]: https://en.wikipedia.org/wiki/Infomercial#TiVo

Here's a recent attempt to load code via video recordings of a TV show from the 80s. It wasn't an easy task. From the Youtube channel Retro Recipies:

Decoding A Program Sent From The Past: https://www.youtube.com/watch?v=MezkfYTN6EQ

Did We Decode A Program Sent From The Past?: https://www.youtube.com/watch?v=VRcs_TUpQ6g

ACTUALLY Receiving A Program Sent From The Past!:https://www.youtube.com/watch?v=jm0EACgCbM0&t=1203s

There was also a backup system for PCs that used a TV interface card, and you connected your computer to a VCR to hold the data. Data was stored in white scanlines on top of a black background. Probably not the most efficient way to store data over NTSC (or PAL) video.

Also from the same web site:

https://newslttrs.com/yes-in-the-1980s-we-downloaded-games-f...

I remember for a short time Computer Chronicle would have a segment where they flashed what looked like static on the screen to transmit programs. You had to have some device to capture it and send it to a computer.

Edit: It looks like it was the followup to Computer Chronicles: Net Cafe https://cyborganthropology.com/TV_Modem