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<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>