Hi David,
Thank you for reporting this problem.
It will be fixed in the upcoming R1 2020 SP1 release.
What you can do now to solve the issue is to set EnableAriaSupport="true", also set the Title property and to call the OnClientLoad function in the OnClientReady event as shown below:
<script>
function OnClientLoad(sender) {
$telerik.$("button[title]").each(function () {
this.setAttribute("aria-label", this.getAttribute("title"));
});
}
</script>
<telerik:RadMediaPlayer OnClientReady="OnClientLoad" Title="My Video" RenderMode="Lightweight" ID="RadMediaPlayer1" Skin="Bootstrap" runat="server" Width="340" BackColor="Black" AutoPlay="true" MimeType="video/mp4" EnableAriaSupport="true"
StartVolume="80" Height="200px">
</telerik:RadMediaPlayer>
Regards,
Rumen
Progress Telerik