jdepoix/youtube-transcript-api ? reverse-engineered prompt

Build me a small Python library that can fetch transcripts and subtitles from YouTube videos without needing an API key or a browser automation setup.

I want to give it a video ID, not a full URL, and get back the transcript as structured objects with the text, start time, and duration. It should work with normal captions and automatically generated subtitles, and it should let me choose a preferred language, with a fallback list if the first one is not available. I also want a way to see what transcript languages exist for a video before fetching one.

Please include a simple command line interface too, so I can test it quickly from the terminal. If possible, support preserving formatting like italics and bold in the transcript text, and make it easy to turn the result into plain raw data when needed. If you need to look up current YouTube transcript behavior or docs online, go ahead.