John Harding, software engineer of YouTube, recently expressed his admiration for HTML5, saying that the new platform has made great progress. However, Harding was quick to clarify that YouTube does not think to leave the Flash, and Adobe's technology still has advantages over HTML5, which make a difference.
First, Flash is required to embedding, and is currently the only way to port the ads and comments embedded in each video. Moreover, HTML5 has not yet solved all the issues he has with microphones and webcams, while scaling to full screen is not always smooth.
It will not be so easy for YouTube to go completely by the Flash in HTML5. Another big issue is that of video standards. This means that YouTube should also support both the H.264 wanted by Microsoft and Apple, and the WebM Google's an emerging power.