Do I have to use only one video format to make use of HTTP streaming videos, or can I choose whichever video file format I want to use?
You can use different video formats, such as Flash (.swf), Windows Media (.wmv), Apple QuickTime (.mov), and MPEG-4(.mp4). It is best to use the most common file formats, and those that can be played on any operating system platform (or at least the most popular ones, such as Microsoft Windows, Mac, and Linux) with easily obtainable free codecs or browser plugins.