NSV (Nullsoft Streaming Video) is an audiovisual container format for streaming video data online. It was created in 2003 by Justin Frankel, while he was still working for Nullsoft. NSV only supports VP3 video codes and MP3 audio, although it was initially designed to stream all audio and video codecs. It is, in fact, the first format to allow users to make and stream live/recorded videos over the internet.
FLV (Flash Video) is a video container format developed by Adobe Systems and comes with a .flv filename format. FLV is primarily used to stream audio, video, and text data such as subtitles. It supports MPEG-4 Part 10 (H.264) video codec and AAC sound.
RealPlayer, Apple QuicTime Player
VLC Media Player