動画のフォーマットはこんな感じ(ちなみに公式動画)

format code extension resolution note
139 m4a audio only DASH audio 49k , m4a_dash container, mp4a.40.5@ 48k (22050Hz)
251 webm audio only DASH audio 102k , webm_dash container, opus @160k (48000Hz)
140 m4a audio only DASH audio 130k , m4a_dash container, mp4a.40.2@128k (44100Hz)
278 webm 256x144 DASH video 95k , webm_dash container, vp9, 30fps, video only
160 mp4 256x144 DASH video 108k , mp4_dash container, avc1.4d400b, 30fps, video only
242 webm 426x240 DASH video 220k , webm_dash container, vp9, 30fps, video only
133 mp4 426x240 DASH video 242k , mp4_dash container, avc1.4d400c, 30fps, video only
243 webm 640x360 DASH video 405k , webm_dash container, vp9, 30fps, video only
134 mp4 640x360 DASH video 411k , mp4_dash container, avc1.4d401e, 30fps, video only
244 webm 854x480 DASH video 752k , webm_dash container, vp9, 30fps, video only
135 mp4 854x480 DASH video 1155k , mp4_dash container, avc1.4d4014, 30fps, video only
247 webm 1280x720 DASH video 1505k , webm_dash container, vp9, 30fps, video only
136 mp4 1280x720 DASH video 2310k , mp4_dash container, avc1.4d4016, 30fps, video only
302 webm 1280x720 DASH video 2646k , webm_dash container, vp9, 60fps, video only
248 webm 1920x1080 DASH video 2646k , webm_dash container, vp9, 30fps, video only
298 mp4 1280x720 DASH video 3465k , mp4_dash container, avc1.4d4016, 60fps, video only
137 mp4 1920x1080 DASH video 4331k , mp4_dash container, avc1.64001e, 30fps, video only
303 webm 1920x1080 DASH video 4410k , webm_dash container, vp9, 60fps, video only
299 mp4 1920x1080 DASH video 5775k , mp4_dash container, avc1.64001e, 60fps, video only
18 mp4 640x360 360p 478k , avc1.42001E, mp4a.40.2@ 96k (44100Hz), 3.07MiB
22 mp4 1280x720 720p 2003k , avc1.64001F, mp4a.40.2@192k (44100Hz) (best)

-f 303+251で落とそうとするとエラーが出て結合に失敗する(ダウンロード自体はできる)