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<!DOCTYPE concept
  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
<concept id="GUID-31FB604F-893D-4829-8C69-F7056C9A0F46" xml:lang="en"><title>Error
Handling</title><shortdesc>The streaming player middleware (the multimedia controller) must
be made aware, when a stream cannot be played because of lack of rights. In
a regular file DRM standard scenario, this task is relatively easy, as the
CAF agent checks whether corresponding rights exist, during instantiation
of <apiname>ContentAccess::CData</apiname>. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
<p>The key stream cannot be decoded in the following scenarios:  <ul>
<li id="GUID-15CAE294-B512-532B-A4A0-679BE57C25D3"><p> <b> Pay-per-view</b>:
The user may have bought rights to view a particular programme, but not the
rights for the programme that follows it on the same channel. Thus, even if
the user had rights when the key stream decoder was instantiated, this may
no longer be the case in 1-2 hours, and the same key stream cannot be decoded
anymore. </p> </li>
<li id="GUID-0BB99E59-4F01-5AED-ABA8-22F137AC0109"><p> <b> Subscription expiry</b>:
The user may have subscribed to the channel, but while viewing the stream,
the subscription expires. Again, the same key stream cannot be decoded anymore. </p> </li>
</ul></p>
<section><title>Limitations</title><p>CAF cannot determine whether a stream
can be decoded during instantiation of the key stream decoder. It only identifies
whether a specific stream is supported and if so, associates it with an appropriate
key stream decoder for decryption of stream data. </p><p>Key stream decoder
cannot determine whether it can decrypt short-term keys, till it receives
key messages. If decrypted information does not reach (or, if for ISMACryp,
it cannot be decrypted), the multimedia controller polls to verify whether
a decoder can decrypt the packets. <xref href="GUID-EE67D14D-1011-3B27-ADEC-C6C192339903.dita#GUID-EE67D14D-1011-3B27-ADEC-C6C192339903/GUID-AF8669AA-BE1B-3FFA-84A2-E54DDDCBC485"><apiname>CKeyStreamDecoder::GetAttribute()</apiname></xref> method
with the <codeph>TAttribute</codeph> parameter <codeph>ECanPlay</codeph> is
used for verification. </p><note>This method allows the controller to query
the key stream decoder whether it has failed to decrypt short-term keys, even
if the decryption process fails and the multimedia controller does not have
any plaintext data. <p>If the decoder cannot decrypt the key packets, it must
drop them and must not push the information to the multimedia controller.</p></note> 
   </section>
</conbody><related-links>
<link href="GUID-6AEA1BCF-EF19-5F6A-9452-E1149C949727.dita"><linktext>Using Streaming
CAF</linktext></link>
</related-links></concept>