html - How does a YouTube movie downloader work? - YouTube

Question

I'm wordering how apps such as Video DownloadHelper work.

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Any ideas?

Answer 1

UPDATE: This answer may now be outdated, see comments below. This was going to happen eventually anyway, as YouTube phases out FLV and shifts toward HTML5 video...

They simply resolve the link to the actual FLV file, and download it.

This is done by copying the video identifier from the URL:

http://www.youtube.com/watch?v=WEeqHj3Nj2c

Which is used to request info about the video:

http://www.youtube.com/get_video_info?&video_id=WEeqHj3Nj2c

The video info includes a TOKEN, which you can then you use to make another request:

http://www.youtube.com/get_video?video_id=WEeqHj3Nj2c&t=TOKEN

If all goes well, YouTube will respond with HTTP 303 See Other, including a Location header with a direct link to the FLV file.