Your best bet is to see what formats youtube-dl returns by running at a command-line,
youtube-dl -F URL
which will produce output looking like this
format code extension resolution note
249 webm audio only DASH audio 53k , opus @ 50k (48000Hz), 4.25MiB
250 webm audio only DASH audio 72k , opus @ 70k (48000Hz), 5.53MiB
140 m4a audio only DASH audio 128k , m4a_dash container, mp4a.40.2@128k (44100Hz), 10.75MiB
251 webm audio only DASH audio 139k , opus @160k (48000Hz), 10.81MiB
171 webm audio only DASH audio 146k , vorbis@128k (44100Hz), 10.04MiB
160 mp4 256x144 DASH video 113k , avc1.4d400c, 25fps, video only, 9.28MiB
278 webm 256x144 DASH video 118k , webm container, vp9, 25fps, video only, 8.97MiB
133 mp4 426x240 DASH video 250k , avc1.4d4015, 25fps, video only, 20.77MiB
242 webm 426x240 DASH video 259k , vp9, 25fps, video only, 18.48MiB
243 webm 640x360 DASH video 472k , vp9, 25fps, video only, 33.50MiB
134 mp4 640x360 DASH video 633k , avc1.4d401e, 25fps, video only, 30.28MiB
244 webm 854x480 DASH video 829k , vp9, 25fps, video only, 56.73MiB
135 mp4 854x480 DASH video 1159k , avc1.4d401e, 25fps, video only, 58.66MiB
247 webm 1280x720 DASH video 1635k , vp9, 25fps, video only, 111.08MiB
136 mp4 1280x720 DASH video 2316k , avc1.4d401f, 25fps, video only, 108.68MiB
248 webm 1920x1080 DASH video 2930k , vp9, 25fps, video only, 206.66MiB
137 mp4 1920x1080 DASH video 4313k , avc1.640028, 25fps, video only, 194.91MiB
17 3gp 176x144 small , mp4v.20.3, mp4a.40.2@ 24k
36 3gp 320x180 small , mp4v.20.3, mp4a.40.2
5 flv 426x240 small , h263, mp3 @ 64k
43 webm 640x360 medium , vp8.0, vorbis@128k
18 mp4 640x360 medium , avc1.42001E, mp4a.40.2@ 96k
22 mp4 1280x720 hd720 , avc1.64001F, mp4a.40.2@192k (best)
Looks like AAC, Opus, Vorbis, MP3 are all used. You can see the containers and most of the bitrates as well.