YouTube is now building its own video-transcoding chips

> No one truly knows the depths of YouTube's video codec selection

Well, you can get an idea by using youtube-dl to get information for a specific video. For example:

  youtube-dl -F "https://www.youtube.com/watch?v=rYEDA3JcQqw"

> AV1 is experimentally available on YouTube

No, it's in production. You've probably played a lot of AV1 video on your desktop machine without realising it. Firefox on my desktop defaults to AV1. To see which codec you're using, right click on the video and select "Stats for Nerds" from the context menu.

The video above has these three encodes for 1080p video:

  mp4  937k  av01.0.08M.08 26.12MiB
  webm 1411k vp9           39.35MiB
  mp4  2696k avc1.640028   75.18MiB

AV1 is the clear winner on file size. The quality is about the same for all three encodes. Each one has different encoding artifacts.

This article is about the second-gen Argos chips.

From the CNET interview, the first-gen Argos silicon was installed in Google’s datacenters in 2015, which likely means Google began development by 2013 at the latest—so about seven years ago.

So the "now" in the title is wrong