Jean-Rene,
Can I assume you're on a Windows system? H.265 playback on a Windows system depends on a couple of things.
a. Please look up the Windows HEVC codec from Microsoft.
b. If the HEVC codec is 10-bit encoded, you will additionally need Davinci Resolve Studio. The studio version also supports hardware accelerated playback and encode for supported H.264 and HEVC profiles.
Givne the dependence on hardware and OS, I would highly encourage you to detail your setup (
see FAQs).
Regards
Shrinivas