I uploaded a mp4, but I can't use the URL in a HTML video-tag

Question

I uploaded a mp4 video via the portal to my trial version Azure account.  I then published it.  I then encoded it.  This produced an output file.  I then published that output file.  Then I copied the URL, and tried to play it in
my browser by pasting it in the address bar.  I got an error that I can't explain - can you?:
<?xml version="1.0" encoding="UTF-8"?>
-<Error><Code>AuthenticationFailed</Code><Message>Server failed to authenticate the request. Make sure the value of Authorization header is formed correctly including the signature. RequestId:1190a24a-860d-4c26-9948-6334393e4e9a Time:2013-10-07T19:41:29.5702692Z</Message><AuthenticationErrorDetail>Signature fields not well formed.</AuthenticationErrorDetail></Error>

Answer 1

I found out what is happening.  When my website asks the user for his URL, which can be a YouTube URL, or a URL of a video / audio on a server, it checks that the URL is valid, and there really is a video or audio at that address.   This does
not work with Azure. 
Public Function UrlExists(ByVal url As String, ByRef Explanation As String) As Boolean
Dim URLReq As HttpWebRequest
Dim URLRes As HttpWebResponse
Explanation = ""
Try
URLReq = CType(WebRequest.Create(url), HttpWebRequest)
URLRes = CType(URLReq.GetResponse(), HttpWebResponse)
If (URLRes.StatusCode = HttpStatusCode.OK) Then
Return True
End If
Catch ex As Exception
Explanation = ex.Message
Return False
End Try
Return (False)
End Function
The code gives the (403) forbidden error in that case. I can suppress this test whenever the input is an Azure URL, but it does raise a question - is there any way to test that the azure URL that the user is using is real?
On another topic, my website also plays audio mp3 files, but Azure Media Services doesn't seem to be able to cope with those.
Thanks,
Gideon