Is there a general purpose solution to increase the speed of arbitrary (embedded) flash videos (Youtube, vimeo, etc)?
I'm not sure about arbitrary embedded Flash videos, but for YouTube, I used to use this Chrome Extension that replaces the Flash player with a VLC player. Playback is much smoother.
Unfortunately this extension is not working at the moment, not until VLC fixes their Lua script. So now I use this, which basically enqueues the selected YouTube video into my current queue in VLC (it needs to be running or the extension will fail).
You can probably try alternative Flash players, like