Hi smile,
Refer below code.
HTML
Master page
<!DOCTYPE html>
<html>
<head runat="server">
<title></title>
<asp:ContentPlaceHolder ID="head" runat="server">
</asp:ContentPlaceHolder>
</head>
<body>
<form id="form1" runat="server">
<div>
<audio controls autoplay style="display:block;">
<source src='<%= ResolveUrl("~/Files/sample.mp3") %>' type='audio/mpeg' />
</audio>
<asp:ContentPlaceHolder ID="ContentPlaceHolder1" runat="server">
</asp:ContentPlaceHolder>
</div>
</form>
</body>
</html>
Content page
<asp:Content ID="Content1" ContentPlaceHolderID="head" runat="Server">
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="ContentPlaceHolder1" runat="Server">
</asp:Content>
Screenshot
