yt-dlp is an actively maintained fork of youtube-dl and is the best way to download high quality videos from YouTube. Instructions for how to install it are located here. The tool has a large API surface area and dense documentation which can result in a frustrating experience when you just want to download a video. If you see it, like it, want it, this guide will help you get it.
yt-dlp -F https://www.youtube.com/watch?v=v7bnOxV4jAc
[youtube] v7bnOxV4jAc: Downloading webpage
[youtube] v7bnOxV4jAc: Downloading android player API JSON
[info] Available formats for v7bnOxV4jAc:
ID EXT RESOLUTION FPS │ FILESIZE TBR PROTO │ VCODEC VBR ACODEC ABR ASR MORE INFO
────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
sb2 mhtml 48x27 │ mhtml │ images storyboard
sb1 mhtml 80x45 │ mhtml │ images storyboard
sb0 mhtml 160x90 │ mhtml │ images storyboard
139 m4a │ 1.63MiB 48k https │ audio only mp4a.40.5 48k 22050Hz low, m4a_dash
249 webm │ 1.70MiB 51k https │ audio only opus 51k 48000Hz low, webm_dash
250 webm │ 2.23MiB 66k https │ audio only opus 66k 48000Hz low, webm_dash
140 m4a │ 4.31MiB 129k https │ audio only mp4a.40.2 129k 44100Hz medium, m4a_dash
251 webm │ 4.35MiB 130k https │ audio only opus 130k 48000Hz medium, webm_dash
17 3gp 176x144 12 │ 2.48MiB 74k https │ mp4v.20.3 74k mp4a.40.2 0k 22050Hz 144p
394 mp4 256x144 24 │ 2.24MiB 67k https │ av01.0.00M.08 67k video only 144p, mp4_dash
160 mp4 256x144 24 │ 2.58MiB 77k https │ avc1.4d400c 77k video only 144p, mp4_dash
278 webm 256x144 24 │ 2.65MiB 79k https │ vp9 79k video only 144p, webm_dash
395 mp4 426x240 24 │ 4.21MiB 126k https │ av01.0.00M.08 126k video only 240p, mp4_dash
133 mp4 426x240 24 │ 5.55MiB 166k https │ avc1.4d4015 166k video only 240p, mp4_dash
242 webm 426x240 24 │ 5.02MiB 150k https │ vp9 150k video only 240p, webm_dash
396 mp4 640x360 24 │ 8.54MiB 256k https │ av01.0.01M.08 256k video only 360p, mp4_dash
134 mp4 640x360 24 │ 11.60MiB 348k https │ avc1.4d401e 348k video only 360p, mp4_dash
18 mp4 640x360 24 │ 20.13MiB 604k https │ avc1.42001E 604k mp4a.40.2 0k 44100Hz 360p
243 webm 640x360 24 │ 10.59MiB 317k https │ vp9 317k video only 360p, webm_dash
397 mp4 854x480 24 │ 15.09MiB 453k https │ av01.0.04M.08 453k video only 480p, mp4_dash
135 mp4 854x480 24 │ 19.31MiB 579k https │ avc1.4d401e 579k video only 480p, mp4_dash
244 webm 854x480 24 │ 18.65MiB 560k https │ vp9 560k video only 480p, webm_dash
398 mp4 1280x720 24 │ 29.73MiB 892k https │ av01.0.05M.08 892k video only 720p, mp4_dash
136 mp4 1280x720 24 │ 32.38MiB 972k https │ avc1.4d401f 972k video only 720p, mp4_dash
22 mp4 1280x720 24 │ ~ 37.52MiB 1101k https │ avc1.64001F 1101k mp4a.40.2 0k 44100Hz 720p
247 webm 1280x720 24 │ 36.24MiB 1088k https │ vp9 1088k video only 720p, webm_dash
399 mp4 1920x1080 24 │ 51.84MiB 1557k https │ av01.0.08M.08 1557k video only 1080p, mp4_dash
137 mp4 1920x1080 24 │ 85.67MiB 2573k https │ avc1.640028 2573k video only 1080p, mp4_dash
248 webm 1920x1080 24 │ 62.54MiB 1878k https │ vp9 1878k video only 1080p, webm_dash
400 mp4 2560x1440 24 │ 147.01MiB 4415k https │ av01.0.12M.08 4415k video only 1440p, mp4_dash
271 webm 2560x1440 24 │ 165.17MiB 4961k https │ vp9 4961k video only 1440p, webm_dash
401 mp4 3840x2160 24 │ 284.63MiB 8549k https │ av01.0.12M.08 8549k video only 2160p, mp4_dash
313 webm 3840x2160 24 │ 405.50MiB 12180k https │ vp9 12180k video only 2160p, webm_dash
Do not rely on the (best) note. Follow this simple algorithm instead.
Applying the algorithm to the example results in 313 and 251. I chose webm because I find it looks and plays better than mp4.
yt-dlp -f 313+251 https://www.youtube.com/watch?v=v7bnOxV4jAc
[youtube] v7bnOxV4jAc: Downloading webpage
[youtube] v7bnOxV4jAc: Downloading android player API JSON
[info] v7bnOxV4jAc: Downloading 1 format(s): 313+251
[download] Destination: [MV] IU(아이유)_LILAC(라일락) [v7bnOxV4jAc].f313.webm
[download] 100% of 405.50MiB in 00:09
[download] Destination: [MV] IU(아이유)_LILAC(라일락) [v7bnOxV4jAc].f251.webm
[download] 100% of 4.35MiB in 00:00
[Merger] Merging formats into "[MV] IU(아이유)_LILAC(라일락) [v7bnOxV4jAc].webm"
Deleting original file [MV] IU(아이유)_LILAC(라일락) [v7bnOxV4jAc].f251.webm (pass -k to keep)
Deleting original file [MV] IU(아이유)_LILAC(라일락) [v7bnOxV4jAc].f313.webm (pass -k to keep)
I used ffmpeg, a dependency of yt-dlp, to make the loop above.
ffmpeg -i input.mp4 -filter_complex "[0:v]reverse,fifo[r];[0:v][r] concat=n=2:v=1 [v]" -map "[v]" output.mp4
The command concatenates a reversed version of the clip to itself.