Comment by web0_cc

yt-dlp ${youtube_video_url} --get-url

ffmpeg -ss ${seconds} -i "${first_url_from_yt-dlp}" -t 1 -r 4/1 -q:v 2 -vf scale="0:-1" ${target}

-r 4/1: 4 frames per second

Again this app is for mobile devices which lack yt-dlp+ffmpeg