Enable d3d12va

[gitoss]

This is trivial, but I'm not versed in creating PR (sorry): ffmpeg now has is support for d3d12va video decoding - see the the d3d12va files in https://github.com/FFmpeg/FFmpeg/tree/master/libavcodec

By default, dxva2, d3d11va and d3d12va are set to autodetect: https://github.com/FFmpeg/FFmpeg/blob/master/configure

But esp. if compiling for generic systems it makes sense to explicity enable it just like dxva2 and d3d11va in the bat (ffmpeg_options_builtin= line).

From https://patchwork.ffmpeg.org/project/ffmpeg/list/?series=9044
"With the Direct3D 12 video decoding support, we can render or process the decoded images by the pixel shaders or compute shaders directly without the extra copy overhead, which is beneficial especially if you are trying to render or post-process a 4K or 8K video."

[L4cache]

Just enable it in ffmpeg_options.txt

[gitoss]

Just enable it in ffmpeg_options.txt

Sure, I just posted this ticket so other people don't have to, but it make it into the original source (even w/o a pr from me).