Short answers, pulled from the story.
The Silent Hill HD Collection contains remastered ports of Silent Hill 2 (2001) and Silent Hill 3 (2003). The compilation excludes the original Silent Hill, Silent Hill 4: The Room, and Silent Hill: Origins.
Hijinx Studios developed the Silent Hill HD Collection for publisher Konami Digital Entertainment. The project took more than two years to complete.
Konami had not properly archived the final source code for Silent Hill 2 or Silent Hill 3. Hijinx Studios had to work with incomplete code, which meant the team encountered bugs the original developers had already fixed, in addition to new issues arising from the porting process itself.
New voice actors were brought in and directed by Mary Elizabeth McGlynn to re-record dialogue for both games. The original Silent Hill 2 voice actor Guy Cihi refused to allow his performance to be reused because he believed Konami owed him residuals, leading to a dispute that eventually resulted in the original voice acting being included as an optional track for Silent Hill 2 only.
The compilation was released on the 20th of March 2012 in North America, March 29 in Japan, March 30 in Europe, and April 5 in Australia. It had originally been announced at the Electronic Entertainment Expo in 2011 with an expected fall 2011 release.
A patch addressing frame rate, fog, and audio-syncing issues was released for the PlayStation 3 version in July 2012. A proposed patch for the Xbox 360 version was canceled in August 2012. The Xbox 360 edition was made backwards compatible with the Xbox One in July 2018.