Here is a list of all documented files with brief descriptions:

va.h	The Core API
va_dec_hevc.h	The HEVC decoding API
va_dec_jpeg.h	The JPEG decoding API
va_dec_vp8.h
va_dec_vp9.h	The VP9 decoding API
va_enc_h264.h	The H.264 encoding API
va_enc_hevc.h	The HEVC encoding API
va_enc_jpeg.h	JPEG encoding API
va_enc_mpeg2.h	The MPEG-2 encoding API
va_enc_vp8.h	VP8 encoding API
va_enc_vp9.h	VP9 encoding API
va_fei.h	The FEI encoding common API
va_fei_h264.h	The FEI encoding H264 special API
va_fei_hevc.h	The FEI encoding HEVC special API
va_vpp.h	The video processing API