Wikipedia
SubViewer
SubViewer is a utility for adding and synchronizing subtitles to video content. It was created by David Dolinski in 1999, and offered for download on his personal website, 1. A friend of David Dolinski (alias Brain) created, at the same time, software to extract subtitles from DVD named SubRip.
SubViewer became popular when support for it was included in the DivX media player. On August 28 2008, YouTube included support for SubViewer and SubRip, allowing existing videos to be retroactively subtitled.