Posted 29 February 2012 - 08:12 PM
Well, first, you don't need to use a feature slider to embed a Youtube video on a homepage or in any posts or pages. Thus, your goal of resizing isn't really necessary. However, if you prefer to use the slider, here's the way.
Make sure you know the dimensions of your slider. Let's say for example the slider is 600px wide and 360px high. When you go to Youtube and select the video, click the option to "Share" the video. A code will appear and a button near it, labelled "Embed". Another box of code will appear when you click the button. Below that, there will be 4 check-box options. Select the last of them "Use old embed code". Below it, you'll see 4 diagrams of various sizes and 1 at the end where you can include the size. Enter the width and the height will appear for you. Copy the code and make a note of the height.
Return to your site's admin section and adjust the slide height to match the one shown on Youtube. Then, in the Media section of your slide setup, paste the Youtube code, as you already know to do. Your video and slide will match.
Make sure you do not have a transition set for your slide or it will move in the middle of your video playing. This is why just embedding the code is easier and better.