Use a local web server as a file cache for YouTube videos with VRChat.
VRChat only uses YouTube-dl to return the raw mp4 video URL, so you can replace the YouTube-dl.exe with your own to return your own custom URL. A caveat of this is that you will need to update your own version of YouTube-dl the inculed Windows php script will auto update YouTube-dl every 3 days, for Linux you will need to do that yourself with whatever package manager you use.
Also you will need to set your YouTube-dl exe as read only otherwise the game with think it's out of date and overwrite it on startup.
To install edit Program.cs to point to your web servers IP address then compile the exe, overwrite %AppData%\..\LocalLow\VRChat\VRChat\Tools\youtube-dl.exe with the built exe and set youtube-dl.exe as readonly to stop VRChat from replacing it.
Put VRCYoutubedl.php on your web server in the directory/parent directory that contains the videos.