In post 2, BROseidon wrote:
Why does that necessitate another tag? Is php that bad or w/e?
A gifv isn't actually an image, and can't be displayed using an image HTML tag for that reason. It's not even a file format, really, just a convention that several image hosting sites use to treat image-like videos and images the same way. What's actually happening behind the scenes is that the site is serving up a video (the same sort of thing you'd get on, say, YouTube) made to look like an image and have a similar appearance to how, say, a GIF looks. However, although you can trick the user into thinking it's an image, you can't really trick the web browser or it wouldn't be able to display it.
(The reason why people use videos rather than images for this is that they compress much better, so they use less bandwidth for both the image hoster and the person looking at the video.)
Of course, it's possible to just detect the .gifv extension and use a different HTML tag to correspond to the BBcode [img] tag. However, you'd need a special case for it, as the two things are fundamentally not the same.