For those of you reading that didn't read the comments above, myself and OP are both aware that this is not how you use a template engine. He seems to have his reasons for wanting to do this directly in the template rather than a plugin or ahead of time in his code. So don't slag me for demonstrating how, please :)
Here is how you can do it in Smarty.
{"http://youtube.com/get_video_info?video_id=`$videoId`"|file_get_contents|parse_str:$result}
{$result.title}
I did the first part all in one call but if you want to be careful you can split it into multiple calls with checks. But I tested this locally and it worked fine.