Thanks for the input. I use less than 1 week ago git/hg pulls of x264, X265, ffmpeg and vlc, but somehow, vlc can't read hvc1 codec, even though I asked for libx265 support in configure. Got to dig a bit deeper there.
Anyway I managed to create HEVC files in mov format with ffmpeg, and could play them with ffplay. Thanks to JS987 "-x265-params" tip, I encoded several 1080p files with crf=20, the same I use for AVC with x264, and indeed the quality seems equal visually but the file size is quite smaller, between 57% to 69% of the AVC file, knowing that there are AAC sound tracks that have the same size in both files.
So that's really an impressive reduction in size for the same quality.
But it's dead slow to create : I'm running between 1.5 to 3 frames per second on a 3.4GHz quad-core AMD Kaveri, about 5 to 10 times slower than wth AVC. I hope optimizations are on their ways...
h265 runs with about 1 fps with 720p on a i5. the same encode runs on h264 with 14 fps.