Of course, these metrics aren't perfect but you can use them as a rough guide to establish equivalence. So, run the command once with the x264 output and once with x265 and compare with different x265 outputs, till you get similar measures. This will allow you to transcode H.265 easily for players that dont support it (your web browser). I would recommend getting a new Intel CPU with Quicksync. The final lines of the console output will contain: SSIM Y:0.984483 U:0.980458 V:0.980921 All:0.983219 (17.751712) H.265 is more efficient which means smaller file size for the same quality, but you wouldnt want to encode a file already encoded in H.264 to H.265.

That said, you can try to establish your own calibration between the current versions of the encoding libraries in your ffmpeg by running the following command, which executes two popular video quality metrics: ffmpeg -i encoded-video.mp4 -i reference-video.mp4 -lavfi 'ssim psnr' -f null. But x265 is not yet as mature in its development as x264, so take that CRF equivalence with a pinch of salt.

x265 CRF 28 is supposed to be e quivalent to x264 CRF 23.

The CRF scales for x264 and x265 do not correspond.

Ffmpeg h265