展示可获得的视频源：
youtube-dl -F https://www.youtube.com/watch?v=D6tC1pyrsTM
[youtube] D6tC1pyrsTM: Downloading webpage [youtube] D6tC1pyrsTM: Downloading video info webpage [info] Available formats for D6tC1pyrsTM: format code extension resolution note 249 webm audio only DASH audio 75k , opus @ 50k, 32.65MiB 250 webm audio only DASH audio 93k , opus @ 70k, 42.86MiB 140 m4a audio only DASH audio 132k , m4a_dash container, mp4a.40.2@128k, 76.19MiB 171 webm audio only DASH audio 152k , vorbis@128k, 69.31MiB 251 webm audio only DASH audio 165k , opus @160k, 82.32MiB 278 webm 256x144 144p 102k , webm container, vp9, 24fps, video only, 54.03MiB 160 mp4 256x144 144p 113k , avc1.4d400c, 24fps, video only, 37.06MiB 242 webm 426x240 240p 246k , vp9, 24fps, video only, 109.85MiB 133 mp4 426x240 240p 255k , avc1.4d4015, 24fps, video only, 83.05MiB 243 webm 640x360 360p 433k , vp9, 24fps, video only, 210.91MiB 134 mp4 640x360 360p 754k , avc1.4d401e, 24fps, video only, 257.75MiB 244 webm 854x480 480p 848k , vp9, 24fps, video only, 394.81MiB 135 mp4 854x480 480p 1390k , avc1.4d401e, 24fps, video only, 558.05MiB 247 webm 1280x720 720p 1829k , vp9, 24fps, video only, 822.81MiB 136 mp4 1280x720 720p 2794k , avc1.4d401f, 24fps, video only, 1.12GiB 248 webm 1920x1080 1080p 3435k , vp9, 24fps, video only, 1.45GiB 137 mp4 1920x1080 1080p 5281k , avc1.640028, 24fps, video only, 2.07GiB 271 webm 2560x1440 1440p 9186k , vp9, 24fps, video only, 4.66GiB 313 webm 3840x2160 2160p 18778k , vp9, 24fps, video only, 10.16GiB 17 3gp 176x144 small , mp4v.20.3, mp4a.40.2@ 24k, 44.14MiB 36 3gp 320x180 small , mp4v.20.3, mp4a.40.2, 127.83MiB 18 mp4 640x360 medium , avc1.42001E, mp4a.40.2@ 96k, 425.86MiB 43 webm 640x360 medium , vp8.0, vorbis@128k, 454.82MiB 22 mp4 1280x720 hd720 , avc1.64001F, mp4a.40.2@192k (best)
下载并合并音视频：
youtube-dl -f 137+251 https://www.youtube.com/watch?v=D6tC1pyrsTM
这样4k的视频都能下载下来了。