While your video is being transcoded, you'll see a red 'Processing' to the right of its title on the My Vids page.
Also, if you go into the Edit Page, you'll see a message on top of the video that tells you it's not ready yet.
You won't be able to grab your embed code until the video is done transcoding.
Once you don't see the red message, can go into your video and see the transcoding message is gone, and can grab the embed code, that's when your video is done transcoding.
Please note this process may take up to 30 minutes for some files.