system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: how can old TV shows that were filmed pre-HD can be syndicated in 16:9 HD when it was originally aired in 4:3 SD and look great for that matter?

I'm watching an Ep of Seinfeld right now from mid 90's that looks great and in Dolby digital 5.1. I have even seen SE01 of this look just as good.
gpt
They were shot on 35mm film, which is far higher in quality than even Blu-ray. They were broadcast as a lower-quality SD version. Now they're being broadcast as a lower-quality HD version. In the future, they will be broadcast as a lower-quality ultra-HD version.