It was about four years ago when I actually tested the autoplay feature of the object element in web browsers. At that time, the only browser that supported it through the param element was Internet Explorer. Now things are radically changed: Firefox, Safari, Chrome and Opera all support this feature, so that the use of the embed element is no longer required for that purpose.
The following code works fine now:
<object data="video.mp4" type="video/mp4" width="600" height="400"> <param name="autoplay" value="true" /> </object>
The major drawback with using object is that you still need plugins to make it work in web browsers. Anyway, the autoplay feature works, but it's surely better to stick to native video support using the video element.