Convert an srt timestamp into seconds.

def convert_timestamp(timestamp):
    """Convert an srt timestamp into seconds."""
    timestamp = timestamp.strip()
    chunk, millis = timestamp.split(',')
    hours, minutes, seconds = chunk.split(':')
    hours = int(hours)
    minutes = int(minutes)
    seconds = int(seconds)
    seconds = seconds + hours * 60 * 60 + minutes * 60 + float(millis) / 1000
    return seconds