[saltminer]

> Ok, but where does this table come from when we need to save a file? It would be a big complication if you had to construct, and transmit 64 independent numbers as a parameter. Instead, most encoders provide a simple interface to set all 64 values simultaneously. This is the well known “quality,” which value could be from 0 to 100. So, we just provide the encoder desired quality and it scales some “base” quantization table. The higher quality, the lower values in quantization table.

I never really thought about how that "quality" slider worked (besides making the compression lossier), but it makes perfect sense now! It always amazes me how much I take for granted.

I always treat compression like a black box: "-crf 23" for H264, PNG and FLAC are nice but MP3 320s and 90+ "quality" JPEGs are good compromises, etc. And that's just for the stuff I deal with, there's no telling how much lossy compression goes on behind the scenes on my own computers, let alone all the stuff served up over the internet. There's so much lossy compression in the world, from EP speed on VHS tapes to websites reencoding uploaded images to every online video ever, it's crazy to think about.