FIRST JAKSTA HAS NEVER WORKED ON YOUTUBE WHICH IS ONE OF THE MAIN REASONS I BOUGHT IT.
SECOND IT USED TO WORK ON MOST OTHER SITES. NOW IT WILL NOT PICK UP ANY STREAM NO MATTER WHAT SITE I AM ON. I HAVE HAD NO LUCK DOWNLOADING ANYTHING. I AM ON EL CAPITAN.
The reason that your Jaksta is not working and has not worked for a long time is almost definitely because you are running a very outdated version.
I would suggest that you first update to the last build we released for 1.X version. You can get the installer here: http://download.shedworx.com/jaksta/beta/Jaksta-1.5.1.pkg
I will send you your activation key privately by email.
If it still does not work then upgrading it to the new 2.0 version that we have just recently released will probably be the next best option. This is a PAID upgrade, but there is a discounted upgrade offer for existing users. You can gain access to it by following the instructions in the in-app update checker window that should appear either automatically or when prompted to do an update check.
I have emailed you the information you will need to go ahead with the discounted upgrade.