Viddy is an iPhone app that beatify your video, kind of like Instagram for video.
Viddy API is done very nicely, made with Mashery, so you can use the same Mashery credentials to log in. Their interactive doc is also great to use, and seems like they implemented using Wordnik framework, as opposed to Mashery's.
Developers now got to work with more restrictions, display guidelines, ads guidelines, etc.. As many of the third-party apps are competing directly with Twitter's client (iPhone/Mac), it is of no surprise that the Twitter's board are making life hard for them.
It is funny that as a service becomes popular, it's API becomes less useful.