2 HN users recommended this explainer2 months2022–2025score 2
Years with an HN recommendation, 2007–2026
HN uses it as a quick, accessible introduction to the black hole star concept in threads about early-universe black holes.
Kurzgesagt explains black hole stars, a hypothesized kind of giant star with a black hole at its core that could be a route to early supermassive black holes.
“Just in case you somehow don’t know what a Black Hole Star is, check out Kurzgesagt’s video about them” (HN, 2025)
If you want an CLI version of a similar idea, you can use yt-dlp and some simple jq to pull down the captions for a file: curl `\ yt-dlp -j [this video] | \ jq -r '.automatic_captions.en[] | select(.ext=="json3") | .url'`
#!/bin/sh ttml2srt() { x=$(echo x|tr x '\34'); tr -d '\34' \ |sed -n "/<p begin/ { s/<p begin=\"//; s/\" end=\"/ --> /; s/\" style=\"s2\">/$x/; s#</p>##p;}" \ |sed = \ |sed "/$x/!s/^/$x/" \ |tr '\34' '\12' \ |sed '/[ ]-->[ ]/s/\./,/g' } read x; case $x in [link] | [link] | [link] | [link] f=$ {x##*=};f=$ {f##*/};case $ {#f} in 10|11) curl -4o $f.mp4 $x video=$(tr \ { '\12' < $f.mp4|sed -n "/itag=22/ {s/u0026/\&/g;s/%3D/=/g;s/%2C/,/g;s/%26/\&/g;s/.*url\":\"//;s/\".*//p;}"|tr -d '\134') test $video||exit ttml=$(tr \ { '\12' < $f.mp4 |sed -n '/timedtext/ {s/u0026/\&/g;s/.*:\"//;s/\".*//;s/$/\&fmt=ttml/p;q;}'|tr -d '\134') test $ttml||exit curl -s4 $ttml|ttml2srt > $f.srt exec ffmpeg -v quiet -y -i $video -vf subtitles=$f.srt $f.mp4 esac esac exit The script above, "1.sh", can be used as follows. echo [this video] | 1.sh It will download the captions as .srt and then "hardsub" them into the video as it dowloads the .mp4. NB. This is slow YouTube downloading without using yt-dl/yt-dlp. Obviously, it will not work with commercial videos. The .srt file is saved as [YouTube ID].srt and the video as [YouTube ID].mp4, where [YouTube ID] is a 10 or 11 ASCII character string. The video format is itag=22, i.e., mp4/720p. Not all videos will have 22 of course. I usually try itag=18, mp4/360p, if 22 is not available. Change the format to whatever is preferred. Looking around for a .ttml/.vtt/.srv[1-3] to srt converter I found solutions that required installing Python or some other large scriptin
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