If only it were that simple. I'm not sure what format Android supports for html5 video, or if it even does. Google put out an opinion piece that by default all browsers should support the open source WebM format, which they purchased and then open sourced. I believe this is the default format for the Desktop Chrome browser. Windows will support any format that you've installed a codec for, so if the user has Quicktime installed mp4 should work, if not maybe not. If you supply a fallback of Flash video, then most newer versions of Android should support that.
Good Luck!
ps
You may want to take a look at this.