Heres what I have so far. Where it has the keystrokes for user and pass you’ll have to enter your own cause I’m not giving away mine. 
One problem I’m getting to start is when it goes to the upload page, It leaves another window with the home page opened.
set youtubelogin to "http://www.youtube.com/login"
set youtubeupload to "http://www.youtube.com/upload"
tell application "Safari"
activate
open youtubelogin
set URL of document 1 to youtubelogin
--This subroutine makes sure the page has finished loading -- it expects the page to finish with the "</html"> tag
my waitforload()
end tell
on waitforload()
--check if page has loaded
set loadflag to 0
repeat until loadflag is 1
delay 0.5
tell application "Safari"
set test_html to source of document 1
end tell
try
set zarg to text ((count of characters in test_html) - 10) thru (count of characters in test_html) of test_html
if "</html>" is in text ((count of characters in test_html) - 10) thru (count of characters in test_html) of test_html then
set loadflag to 1
end if
end try
end repeat
end waitforload
tell application "System Events"
keystroke "MY USERNAME"
keystroke tab
keystroke "MY PASSWORD"
key code 36
end tell
tell application "Safari"
activate
open youtubelogin
set URL of document 1 to youtubeupload
my waitforload()
end tell
So yeah when it gets to the upload page I want it to select the upload button. Then, the tricky part. I want applescript to display a browse in a dialog box where I can select a video file to upload. Then, I want dialog boxes where I can type the title, description, and tags and it will put them in the right place. And maybe if it’s possible, it would be great if it could display the progress in a dialog box, but I doubt that’s possible.