Hola.

La grafica si decodifica HEVC. https://en.wikichip.org/wiki/intel/hd_graphics/520

He visto esto en el foro de INTEL sobre la HD520. https://communities.intel.com/thread/116723

Intel® Skylake processors support HW acceleration of VP9 videos at 4k only if it is 24fps, higher frame count will go via Software.

Our development team has confirmed that ultra-low powered processors (i.e 15W TDP) with Intel HD Graphics 520 uses a hybrid HEVC 10bit decoder that it may reach up to 4K 15Mbps 24 fps, thus it would be expected behavior seeing lag on some HEVC media that goes above these specs.

Por si acaso, actualiza drivers de grafica y prueba esto: Blog H T P C: Como activar 4K y HEVC en Media Player Classic HC

Saludos.