Ahmed Nuaman explains on this tutorial at FlashTuts+ how to create a wrapper to allow loading Youtube videos using the YouTube Player into a Flash project using Actionscript 3.0

The Process:

Step 1 – The Plan
Step 2 – Starting the Wrapper
Step 3 – Handling Sandbox and Security Errors
Step 4 – Preparing to Load the Player
Step 5 – Creating the Initialising Function
Step 6 – Loading the Player
Step 7 – Dealing With Events (in AS2)
Step 8 – Resizing the Player
Step 9 – Now the Player’s Ready
Step 10 – Destroying the Player
Step 11 – Stopping the Video
Step 12 – Creating the Wrapper
Step 13 – Using the Wrapper