Hey all - something I put together last night after hearing the news of Google opening up the dev tools.
You can visit, for example, a TED talk, hit the bookmarklet and it will pull down the MP4 behind the scenes and present it on a layer that's now Chromecast friendly. Same goes for Vimeo, Plex.tv (without having to pay the $5/mo) and quite a few other video sites that are most likely against the TOS to link to.
Definitely open to hearing the thoughts of the community!
Good question. I'm not doing anything special other than grabbing the MP4 and sending it to Chromecast, so I assume it's #3. As far as login permissions, I haven't run into any with my brief testing. I would assume since I'm grabbing the MP4 file directly (and sometimes even with the temporary timestamp to allow access to the file) it's not going to be much of an issue. Google put out a LOT of sample code to make this relatively easy to implement. Honestly, coming up with the REGEX that worked across as many sites as possible was the hardest part.
Since Plex transcodes to Chromecast friendly format, this bookmarklet will only cast if your original files are already in MP4, OGG, or WEBM format. So, don't expect your AVI files to cast with the bookmarklet.
Plex is awesome, though, and they deserve that $5/mo for making the Chromecast actually useable.