>>101564389
youtube, I download them as ogg opus with the highest quality (usually ~130) using yt-dlp. then I sync the files from my server to my phone using rsync.
thumbnail embedding sadly doesn't work for some reason, but that doesn't really matter to me.
this is the command I use: yt-dlp "$1" --progress -f 'ba[ext=webm][vcodec=none][acodec=opus]' -o '%(track,title)s.%(ext)s' -x --embed-metadata
where "$1" is the url