NV12 pix_fmt for encoding

[jahwanoh]

Hi is there any way to use encoder with NV12 pixel format? such as a manual patching. currently it is only support YUV420p in this repository.

codec name : h264_nvmpi [h264_nvmpi @ 0x7ea40041b0] Specified pixel format nv12 is invalid or not supported cannot open encoder