What I want to do is execute a mouse click say on youtube to press play when the page loads. How do I click that specific location (assuming it is always in the same location)?<
In general, browsers won't let simulated mouse clicks trigger "real" actions, e.g. a jQuery click() won't cause the browser to follow a link. Otherwise, spammers could trigger banner clicks on every page load (among other more malicious uses).
According to http://www.filosophy.org/2011/03/talking-to-the-web-the-basics-of-html5-speech-input/:
Eventually, it will be possible to invoke the speech-recognition directly with the startSpeechInput() method, but to my knowledge this is not implemented in any of the current browsers.
I suggest waiting for Chrome to implement the API so that you can trigger speech input from JavaScript.