how to change src attribute of HTML5 tag in page

I tried the <video> tag of html5, and it runs the mp4 file OK (If I define the src attribute in the HTML code, however, what I want to do is to pass the video url to the web form as query string, and do not know how to change the src property dynamically. even when I try to user thevideo.attributes.add for the <video> tag marked as runat="server" and ID="thevideo" I get an error showing the ID "thevideo" of the Video element is not known to the code. Can some help please. Thanks
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Daniel Van Der WerkenIndependent ConsultantCommented:
Can we see your HTML and code-behind?

Did you give the video tag the runat="server" attribute? You can't ID (thevideo) won't be available to the code-behind if you don't set the runat="server" attribute in the HTML tag:

<video id="thevideo" runat="server">

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fmichailAuthor Commented:
Sorry Dan7el, you are right, I forgot to add runat="server".. please accept my apologies. Thanks
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