Is loading a video in a browser multithreaded?

It's hard to know what is multithreaded in a browser and what isn't. It seems while a video streams or progressively downloads, it does not affect page performance, so my guess it is.

Note I'm using Flash video, but it's really about video in general. Any other tips on what else is multithreaded (image loads?) is also helpful. I know JavaScript is not, and I thought Flash wasn't but I heard somewhere that it may be (or it could be done), but I think they were not 开发者_StackOverflow中文版well informed.

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flash wmode parameter controls which mode should be used. transparent runs in browser's application domain, and "window" runs as a separate flash player process drawing on width height and x&y specified by browser.

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It's platform and implementation specific. With flash on the MacOS 64 bit (sorry I only know my win platform) flash runs in its own process, so definitely multithreaded. Chrome also runs all plugins on a separate thread.