You can upload your mp4/ogv videos by going to “Media” > Add New. Then go to the post/page editor page and click on “Add external video by URL”. A popup window will be displayed where you can enter the url to your mp4/ogv file.
To be compatible with all browser and use the html5 compatibility and fallback flash, what must I do ? Publish two video with exactly the same name and different extention ? or is there another solution ?