Using the ttsengine Property/Attribute for RTSP Streaming

NOTE: The IP Media Server implementation does not currently support this functionality.

The `ttsengine` property/attribute can also be used to enable RTSP (Real Time Streaming Protocol) streaming.

Then, whenever the application sets the `ttsengine` property/attribute to "RTSPTTS", VoiceGenie will use the content of each `<prompt>` tag as a URI to fetch an RTSP resource. For example:

    <field name="streamField">
       <property name="TTSENGINE" value="RTSPTTS"/>
       <prompt>
          rtsp://rtsp.server.com/audio
       </prompt>
       ...
    </field>

The RTSP module supports the concept of a shareable stream. For a shareable stream, if the incoming URI is the same as another stream already on another call, the stream would simply be shared between the calls, and no additional RTSP requests would be made to the RTSP server. For an unshareable stream, the RTSP server will be contacted every time an RTSP URI is requested.

By default, a URI is shareable. To mark a URI as not shareable instead, add the parameter "shareable=false" to the specified URI. For example:

    <prompt>
       rtsp://rtsp.server.com/audio?shareable=false
    </prompt>

Note: When multiple consecutive RTSP streams are to be played, the application developer should insert an empty audio file between the RTSP URIs. For example:

    <block>
       <![CDATA[
          rtsp://10.0.0.171:8554/sting?shareable=true

       <audio src="empty.vox"/>
    </block>
    <block>
       <![CDATA[
          rtsp://10.0.0.171:8554/welcome?shareable=false

       <audio src="empty.vox"/>
    </block>
    <block>
       <![CDATA[
          rtsp://10.0.0.171:8554/longtts

    </block>