Contains the last utterance duration size in milliseconds.
Example
<?xml version="1.0"?>
<vxml version="2.0">
<property name="recordutterance" value="true"/>
<form>
<field name="first_name">
<prompt bargein="false">
<audio src="en_us/enter_first_name.wav">
Please say your first name and spell it.
</audio>
</prompt>
<grammar src="https://vxml.local.plumvoice.com/grammars/firstname.php" type="application/srgs+xml"/>
<filled>
Your recording is <value expr="first_name$.recording"/>.
The recording size is <value expr="first_name$.recordingsize"/> bytes.
The recording duration is <value expr="first_name$.recordingduration"/> milliseconds.
</filled>
</field>
</form>
</vxml>
