Can We Use Video Tag In Figure Tag In HTML5

Yes, it is possible.

This is the definition of the <figure> tag as specified by W3C:

The figure element represents some flow content, optionally with a caption, that is self-contained and is typically referenced as a single unit from the main flow of the document.

The element can thus be used to annotate illustrations, diagrams, photos, code listings, etc, that are referred to from the main content of the document, but that could, without affecting the flow of the document, be moved away from that primary content, e.g. to the side of the page, to dedicated pages, or to an appendix.

Here you can see an example extracted by W3C documentation, in which a <video> tag is included in a <figure> tag.

<figure>
 <video src="ex-b.mov"></video>
 <figcaption>Exhibit B. The <cite>Rough Copy</cite> trailer.</figcaption>
</figure>

You can find the official W3C documentation here: http://www.w3.org/html/wg/drafts/html/master/grouping-content.html#the-figure-element

Yes you can - according to the HTML5 spec, a <figure> permits flow content (which is comprised of both flow elements & normal character data). Given that <video> & <audio> are both one of the many flow elements, it is perfectly valid for them to be nested within a figure.

This article from HTML5 Doctor seems to suggest the same thing, take a look.