Subject: [speechsc] VoiceXML Compatibility Issues with Synthesis

From: Andrew Wahbe <[email-masked]>
Date: Wed, 07 Dec 2005 16:51:15 -0500

The VoiceXML Forum MRCP Liaison committee is currently evaluating the 
latest MRCP v2 draft to (a) evaluate the compatibility between MRCP v2 
and VoiceXML and (b) generate test assertions for MRCP v2 based VoiceXML 
browsers and MRCP v2 based media resources. We are currently examining 
the Speech Synthesis portion of the specification and have found the 
following issues:

   1. Both the Fetch Hint header (8.4.10) and Audio Fetch Hint header
      (8.4.11) say that they apply to audio files. Which one is it?
      These descriptions should be specific about what resource types
      they apply to.
   2. Audio Fetch Hint header (8.4.11) supports a "stream" value that is
      not supported by VoiceXML 2.x. Moreover, this value says nothing
      about when to fetch the audio file; it determines when it should
      start playing. You could have a "safe" fetch that was either
      streaming or non-streaming. The same applies to a "prefetched"
      audio file.  A separate header should control streaming if
      required. It's worth noting that VoiceXML leaves streaming as a
      platform-specific optimization.
   3. The maxage and maxstale cache control headers are global in MRCP
      while VoiceXML breaks this down by resource type (e.g.
      audiomaxage, audiomaxstale, grammarmaxage, grammarmaxstale, etc.).
      This results in compatibility issues between VoiceXML and MRCP. Is
      there a way to apply these parameters to specific resource types
      in MRCP?
   4. It isn't clear if the  "003 uri-failure" SPEAK completion cause
      applies to referenced SSML files, or audio files or both. If it
      applies to audio files then this is in conflict with the
      VoiceXML/SSML behavior of "continuing processing if audio cannot
      be successfully rendered. The SSML Recommendation says "/If the
      audio
      <http://www.w3.org/TR/2004/REC-speech-synthesis-20040907/#edef_audio>
      element is not successfully rendered, a synthesis processor
      <http://www.w3.org/TR/2004/REC-speech-synthesis-20040907/#term-processor>
      should continue processing and should notify the hosting
      environment./" To truly meet this requirement it would seem that
      we need some way to indicate that audio was not played while
      continuing to play the other audio and SSML specified in the speak
      request. A completion-cause of 003 could perhaps be used to
      indicate this (if we allow the notification of the host
      environment to occur after the request completes), though the
      completion cause is documented as representing the "reason of
      request completion" which wouldn't be accurate in this case. This
      definitely needs some clarification.

If you would like to participate in the VoiceXML Forum MRCP Liaison 
committee please email me.
Thanks,

Andrew Wahbe
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