There is no public driver available on the downloadcenter.intel.com at the moment supporting API 1.19. I don't have timeline on when it will be available, I can let you know that soon.
Anything in particular you are looking for in API 1.19 to test or add that feature in your application?
I am still checking up on the next driver which will support API 1.19. The number of reference frame is a parameter defined in media sdk which enables to have multiple frames as a reference frame to encode the current frame. Theoretically this parameter is designed to improve the quality of the video as the number of reference frame increase so the compression efficiency but decoding such a video can cause slowing of decode as those reference will be in the memory unless all the frames dependent on that are decoded.
There are more parameters like NumRefActive P/BL0/BL1 which are used to specify the number of active reference frame for P and B frames in reference frame list 0 and list 1 where list 0 is for only P & B frames and list 1 is only for B frames.
Hope it helps!
Intel has responded in the past and confirmed that TU1 (Best), TU4 (Balanced), and TU7 (Best Speed) are the only target usages that are supported for HEVC.
Regarding scene changes and VBR, the quality is much worse for fast movement with interlaced content (confirmed for 1080i) than progressive content (confirmed with both 720p and 1080p). Its actually quite good for progressive content. But, disregarding fast movement for interlaced content, HEVC is superior to H.264. I posted about this in another forum post earlier today.
Where did you get 4471? The latest publicly released Intel Graphics package that I can find is 4463, available at https://downloadcenter.intel.com/download/26078/Intel-Graphics-Driver-for-Windows-10-and-Windows-7-8-1-15-40-?product=88357 . This release also includes support for API version 1.19.