Sorry, they're very likely running A/B testing of some sort, as this link was AV1 (Codecs: avc1.64002a (299) / mp4a.40.2 (140)) for me earlier, but no longer:

https://www.youtube.com/watch?v=ogfYd705cRs

avc1 is https://en.wikipedia.org/wiki/H.264/MPEG-4_AVC not AV1

The available formats for that video are:

    $ youtube-dl -F https://www.youtube.com/watch?v=ogfYd705cRs
    [youtube] ogfYd705cRs: Downloading webpage
    [youtube] ogfYd705cRs: Downloading video info webpage
    [info] Available formats for ogfYd705cRs:
    format code  extension  resolution note
    249          webm       audio only DASH audio   70k , opus @ 50k, 37.58MiB
    250          webm       audio only DASH audio   88k , opus @ 70k, 45.92MiB
    140          m4a        audio only DASH audio  136k , m4a_dash container, mp4a.40.2@128k, 98.65MiB
    171          webm       audio only DASH audio  148k , vorbis@128k, 70.46MiB
    251          webm       audio only DASH audio  158k , opus @160k, 95.71MiB
    160          mp4        256x144    144p  114k , avc1.4d400c, 30fps, video only, 29.91MiB
    278          webm       256x144    144p  147k , webm container, vp9, 30fps, video only, 61.11MiB
    242          webm       426x240    240p  226k , vp9, 30fps, video only, 75.75MiB
    133          mp4        426x240    240p  252k , avc1.4d4015, 30fps, video only, 54.98MiB
    243          webm       640x360    360p  413k , vp9, 30fps, video only, 140.49MiB
    134          mp4        640x360    360p  644k , avc1.4d401e, 30fps, video only, 182.59MiB
    244          webm       854x480    480p  764k , vp9, 30fps, video only, 227.69MiB
    135          mp4        854x480    480p 1193k , avc1.4d401f, 30fps, video only, 377.25MiB
    247          webm       1280x720   720p 1521k , vp9, 30fps, video only, 423.38MiB
    136          mp4        1280x720   720p 2375k , avc1.4d401f, 30fps, video only, 730.12MiB
    248          webm       1920x1080  1080p 2674k , vp9, 30fps, video only, 810.25MiB
    137          mp4        1920x1080  1080p 4461k , avc1.640028, 30fps, video only, 1.34GiB
    17           3gp        176x144    small , mp4v.20.3, mp4a.40.2@ 24k, 57.43MiB
    36           3gp        320x180    small , mp4v.20.3, mp4a.40.2, 162.63MiB
    18           mp4        640x360    medium , avc1.42001E, mp4a.40.2@ 96k, 332.87MiB
    43           webm       640x360    medium , vp8.0, vorbis@128k, 452.27MiB
    22           mp4        1280x720   hd720 , avc1.64001F, mp4a.40.2@192k (best)

Ah, my brain missed the 'c', thx for that