Sorry on the delay in getting back to you. Curl extension is simply referering to a library that needs to be included with the installation of PHP running on your server. To Check this open notepad or similar create a file named test.php with the contents:
And then view the file in a browser it will tell you everything about PHP running on your server. Scroll down or ctrl + F to search and look for CURL if its there your server has everything you need.
As for the second question I am not exactly sure what you mean. Are you talking about static picture i.e a picture that shows while the video is not playing?