H.264 is a video compression standard used for HD videos. In fact, it’s the most widely-used video codec today. As such, this codec can be incorporated into several container formats like MP4, 3GP, MOV, FLV, and others. Most of the time, it’s encoded with the Advanced Audio Coding (AAC) codec.
Apple QuickTime Player VLC Media Player Windows Media Player Apple iTunes
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