Complex sentence: The subtitle file format was proposed and invented by an MPlayer developer in 2001 and was not released to the public until it was incorporated into the MPlayer code, whereas the KISS player was released several years later in 2003.
Split into simpler sentences: The subtitle file format was proposed and invented by an MPlayer developer in 2001 and was not released to the public until it was incorporated into the MPlayer code. Whereas the KISS player was released several years later in 2003.