It's much easier to just use jQuery, since this is just a task for university and you do not need to save code.
So, your code will look like:
function sendMyComment() {
$('#addComment').append('<input type="hidden" name="video_id" id="video_id" value="' + $('#video_id').text() + '"/><input type="hidden" name="video_time" id="video_time" value="' + $('#time').text() +'"/>');
$.ajax({
type: 'POST',
url: $('#addComment').attr('action'),
data: $('form').serialize(),
success: function(response) { ... },
});
}