IMAGE
The image size must not wider than 800 pixel in width, if your image wider than 800 pixel you must resize it down.
How to resize your image with PhotoShop : go to image menu/ image size / change the width to 800 pixel, choose bicubic sharper best for reduction.
Then save your image as JPEG (.jpg) format at high (

quality , embed sRGB color profile.
VIDEO
1. Upload video to your YouTube or VIMEO account.
2. Selected your video or playlist and copy your URL from address field of your browser.
Sample :
http://www. youtube.com/watch?v=-HutuMqTAPw
3. Then paste on to your reply text box.
4. It should look like this