When will Brock crawl?

Here is a clip of Brock playing the "I wish I were a frog" game. He is so close to crawling but can't seem to get his arms and legs to work with each other. It's fun for Josh and me to watch him make progress. The push ups were the first step in this process. Then he started getting up on his knees. Then he would jump from a push up to his knees...and now this. Since Brock is our first child it's hard to know how many more steps there are before forward motion. We'll keep you updated.