GOM Player includes many codecs (XviD, DivX, FLV1, AC3, OGG, MP4, H263 and more) so you won't need to install separate codecs for most videos. For those videos that require a separate codec, GOM Player will find one and direct you to a place where you can download open source version of the codec.
GOM Player's that enables users to view files with broken index or that are still being downloaded.