A 2018 Status Update On The Royalty-Free AV1 Video Codec

[quikee]

OK, that makes sense. Did you see Mozilla posting anything about it?

No, my info is mostly from the talk about it on #daala IRC channel on freenode.

[quikee]

Opus came about through a process similar to AV1, where the best aspects of Xiph's CELT and Skype's SILK were combined.

No, Opus is actually two codecs in one package - CELT (general sound) and SILK (speech) + a hybrid mode. AV1 is one codec which will just use some coding tools from other codecs. Coding tools that work well in one codec might not be a good fit for the other. Some of daala coding tools were dropped because of that (for example PVQ or CfL which had to be rethought and is completely different from what daala uses).

[quikee]

It's just that the features with the most publicity came from Daala.

That's because Mozilla folks are good at communicating on what they're doing - visiting conferences and giving talks. Would be great if Google did the same. Actually it would be great if the whole AOM is more open at what they're doing (regarding coding tech used and decisions).

[actinic]

youtube-dl picks the AVC track because it's of higher quality than VP9. Argue with them if you disagree.

Netflix disagrees. MSU disagrees. YouTube disagrees.

[chithanh]

vp9 still hasn't gained any traction besides within company with the hardware to encode it.

VP9 is not a vendor-neutral open standard, it is wholly controlled by Google (case in point: bug in VP9 reference decoder that Google refuses to fix, and therefore every implementor has to replicate it). Hardware manufacturers are understandably wary of spending silicon area for supporting such formats.

Daala/Thor/VP10 proponents recognized this and are working through a standards body with open participation rules (AOmedia) to get AV1 standardized.

[Stebs]

youtube-dl picks the AVC track because it's of higher quality than VP9. Argue with them if you disagree.

What are you talking about?
youtube-dl picks up exactly the video and audio codec you want (thanks to DASH) and then combines them to a video file.

For a given resolution and framerate (like 1080p 60), the bitrate for the avc version on Youtube always is (and also has to be) higher than the vp9 version.
That's no surprise since avc/h264 is an older generation of codec than vp9 (and h265).

One of the multiple tracks is marked as "best" by Youtube (is that what you are referring to?), but that is not the version with the best quality (it is often not even the version with the highest resolution/framerate).
It is the best choice if you are not sure at all what to pick: the version that probably will play with every device and with acceptable quality (not SD).
If you know what you want, it is always better to tell youtube-dl what you want so your download is not unnecessarily big.