Why Quadro P620 does not support H265 Encoding technique ?

I’m using H265 encoding technique on a P620 graphics card.
Using FFmpeg 4.1 version.
Driver details as below,

NVIDIA System Information report created on: 04/18/2019 15:29:05
System name: XXXXXX

Operating System:	Windows 10 Pro for Workstations, 64-bit
DirectX version:	12.0 
GPU processor:		Quadro P620
Driver version:		419.17
Driver Type:		Standard
Direct3D API version:	12
Direct3D feature level:	12_1
CUDA Cores:		512 
Core clock:		1265 MHz 
Memory data rate:	5.01 Gbps
Memory interface:	128-bit 
Memory bandwidth:	80.16 GB/s
Total available graphics memory:	10205 MB
Dedicated video memory:	2048 MB GDDR5
System video memory:	0 MB
Shared system memory:	8157 MB
Video BIOS version:
IRQ:			Not used
Bus:			PCI Express x16 Gen3
Device Id:		10DE 1CB6 12641028
Part Number:		G212 0505


nvui.dll		NVIDIA User Experience Driver Component
nvxdplcy.dll		NVIDIA User Experience Driver Component
nvxdbat.dll		NVIDIA User Experience Driver Component
nvxdapix.dll		NVIDIA User Experience Driver Component
NVCPL.DLL		NVIDIA User Experience Driver Component
nvCplUIR.dll		8.1.940.0		NVIDIA Control Panel
nvCplUI.exe		8.1.940.0		NVIDIA Control Panel
nvWSSR.dll		NVIDIA Workstation Server
nvWSS.dll		NVIDIA Workstation Server
nvViTvSR.dll		NVIDIA Video Server
nvViTvS.dll		NVIDIA Video Server
nvLicensingS.dll		NVIDIA Licensing Server
NVSTVIEW.EXE		NVIDIA 3D Vision Photo Viewer
NVSTTEST.EXE		NVIDIA 3D Vision Test Application
nvDispSR.dll		NVIDIA Display Server
NVMCTRAY.DLL		NVIDIA Media Center Library
nvDispS.dll		NVIDIA Display Server
nvDevToolS.dll		NVIDIA 3D Settings Server
NVCUDA.DLL		NVIDIA CUDA 10.1.112 driver
nvGameSR.dll		NVIDIA 3D Settings Server
nvGameS.dll		NVIDIA 3D Settings Server

I have tried driver having details below,

R418 U4 (425.31)  WHQL 
Release Date: 
Operating System: 
Windows 10 64-bit
English (US) 
File Size: 
392.67 MB

Same thing I have tried on Quadro P2000 and that also not worked for me.
Please suggest what makes this not worked?