I didn't find any plugins, but I've patched jCap to provide a callback and made an add example:
http://github.com/irae/jCaps/blob/master/addsexample.html
$("#myVid").jCaps({
language: 'en',
languageChooser: false,
toggleButton: false,
onButton: false,
offButton: false,
interfaceImg: false,
transcriptButton:false,
showCaptions: true,
transcriptType: 'html',
transcriptsDiv: $('#transcripts'),
subtitleChangeCallback:function(oldV,newV) {
if(!addShown) {
addShown = true;
$('#myVid').get(0).pause();
setTimeout(function(){
$('#captions').text('');
$('#myVid').get(0).play();
},5*1000); // time to show add (5 seconds)
}
}
});
This is not ideal. If I were you, I've started a new plugin from scratch just for that. It's not difficult to build on top of what's jCap already does.