Here's how to enter the link to a YouTube video.

1. go to YouTube.com and find the video you want to embed.
2. on the detail page for the YouTube video, you'll see a box with 2 ways to access the video, URL and Embed. Since we want to embed the video within the Repository module, copy the embed tag and paste it into Notepad. Look at the embed source and you'll see a parameter named movie, copy JUST the value of the movie parameter and paste it into your Repository Upload form in the Video File field.

eg:
Here's the embed value from a YouTube.com video

So, finding the movie parameter, you would copy ONLY the value, not including the quotes.

You can resize the video to whatever size you like :) take a look at the template.html file, you'll see the object tag which embeds the YouTube video, there are 2 places where the width and height of the video are specified, just change the values to whatever size you want.

If you look at the template, you'll see that it includes all of the tags necessary to embed the video with a placeholder for the movie parameter value ( which is what the user enters ). You could remove all of the object and embed tags and just have a single placeholder ( I'd use [SUMMARY] since the length is unlimited ) then allow the users to just copy and paste the entire 'embed' value from the YouTube site into the upload form field.

The problem with them pasting the 'URL' field is that it will open the YouTube video in another browser window. If that's what you want, then that would be fine. But to have the video play within the contents of the Repository module you have to use the 'embed' value.