1. rm Ipython dependence
1. use default base conda env
1. add caption_num_second [use caption_num caption_num_second to get full control](https://github.com/xsthunder/download-youtube-subtitle#use-caption_num-caption_num_second-to-get-full-control)
1. unavailable prompt for invalid video
unavailable video prompt
e.g.
text
ERR: no caption available for this video ;( following are message from youtube
ERR: ['playabilityStatus":{"status":"UNPLAYABLE","reason":"影片無法提供","errorScreen":{"playerErrorMessageRenderer":{"reason":{"simpleText":"影片無法提供"}']
ERR: can't not retrive caption, visit https://youtube.com/get_video_info?video_id=EozTm6ZVf1U for detail
see 8