How do flv downloaders work?

Question

How do browser plugins that enable you to download video from hosting sites that use flash player work? How are they able to get direct link to flv video? Is it possible to do so without actually running flash plugin?

Answer 1

I'm not sure about the browser plugins specifically, but there are standalone programs that can download videos without running a flash plugin, for example youtube-dl and cclive.

Those work by deriving the URL of the .flv from the data the video website is passing into the player. The player of course needs to be able to derive the URL of the actual video based on what it is given, so the downloader simply needs to replicate that logic. In the case of cclive, it is done using Lua scripts, so support for additional players can be added fairly easily. There's a decent number of them here. (cclive uses libquvi.)

A browser plugin may be able to be more general, depending on what APIs the browser provides. For example, if they have the ability to intercept URLs being accessed by plugins, they wouldn't need to replicate the player's logic, but then they would require flash. From what I remember of how plugins work though, flash would be able to fetch the videos bypassing the browser entirely, although whether it does or not is a different issue.