There are many Video Codec’s to choose from when streaming, and decision is not an easy one and is based on a number of factors including the amount compression and the final device the video is aimed for. FLV is a flash video file which has been used for pre-recored video’s for watching over the internet. FLV however doesn’t work on iOS as its a video file based on Flash, thus would be useless if you produced a video or stream intended for the iOS platform.
The current file format of choice for pre-recorded material to be viewed on the web is MP4, with h.264 video codec and AAC audio codec, this is mainly due to the high picture quality to high rate of compression, ideal for streaming. There are many other codecs out there and this link has a list codecs and links to more information about each.