11 March 2016 - WebVTT segment duration

<?xml version="1.0"?>
<query>
    <userid><<id>></userid> <!-- required-->
    <userkey><<key>></userkey> <!-- required-->
    <action>[Action]</action> <!-- required-->
    <format>
        <!-- Format fields -->
        <closed_captions>
            <source>[WebVTTCCSource]</source>
            <mux_type>webvtt</mux_type>
            <vtt_segment_duration>[SegmentDuration]</vtt_segment_duration>
        </closed_captions>
    </format>
</query>

{
    "query": {
        "userid": "<<id>>",
        "userkey": "<<key>>",
        "action": "[Action]",
        "format": {
            "closed_captions": {
                "source": "[WebVTTCCSource]",
                "mux_type": "webvtt",
                "vtt_segment_duration": "[SegmentDuration]"
            }
        }
    }
}