INPUT: array with captions, i.e.
                [{'texlines': [u"So, I'm going to rewrite this", 'in a more concise form as'],
                'time': {'hours':'1', 'min':'2','sec':44,'msec':232} }]
            OUTPUT: srtformated string

def _generateSrt(self,captions):
        """ INPUT: array with captions, i.e.
                [{'texlines': [u"So, I'm going to rewrite this", 'in a more concise form as'],
                'time': {'hours':'1', 'min':'2','sec':44,'msec':232} }]
            OUTPUT: srtformated string
        """
        caption_number = 0
        srt_output = []
        for caption in captions:
            caption_number += 1
            #CAPTION NUMBER
            srt_output.append(str(caption_number))
            #TIME
            time_from = ( caption['time']['hours'], caption['time']['min'], caption['time']['sec'], caption['time']['msec'] ) 
            if len(captions)>caption_number:
                #display caption until next one
                next_caption_time = captions[caption_number]['time']
                time_to = ( next_caption_time['hours'], next_caption_time['min'], next_caption_time['sec'], next_caption_time['msec'] )
            else:
                #display caption for 2 seconds
                time_to = (time_from[0],time_from[1]+2,time_from[2],time_from[3]) 
            srt_output.append( (":").join([str(i) for i in time_from[0:-1]])+","+str(time_from[-1])+" --> "+(":").join([str(i) for i in time_to[0:-1]])+","+str(time_to[-1]))
            #CAPTIONS
            for caption_line in caption['textlines']:
                srt_output.append(caption_line)
            #Add two empty lines to serarate every caption showed
            srt_output.append("")
            srt_output.append("")
        return srt_output