There are some many different devices today in the world and each devices requires a different format of video for it to play properly. For this very reason large events with lots of simultaneous viewers need to make sure that their streaming provider is feeding your video out with live transcoding. If you are looking for a vendor we went ahead and found one. You can view their service description at the url below.
From just a quick overview of the page it appears that they support all of the popular formats. They also offer a different pricing solution that most providers. More than likely some of their broadcasting technology is custom made with allows some sort of price break. They also offer transcoding for hosted videos. They are also passing the savings in the same way by only charging for the main copy for the video.
Mobile devices are by far the ones that most badly require this. So many different type of screens and browsers it would be near impossible to offer only one quality of your stream. You can also opt to send out multiple streams from your desktop encoder but their would put all of the strain and heavy lifting on your computer. If you do happen to go this route you will need a strong computer with a quad-core CPU. Definitely no laptops.