Renderring external texture (from Decklink mini recorder 4K),laggy ,choppy

I plug the Decklink SDK into unity, for capturing realtime image from real camera to a texture2D( create by Texture2D.CreateExternalTexture), then do some composition. But i found the texture2D playback with laggy an choppy. I dont know why, my code have processed the decklink image very smoothly,1080p60, surely uploading raw data of one decklink frame to texture2D on per unity frame (fixed 60fps) .

Maybe it is my reason, then I test VideoPlayer with a mp4 file, the same phenomenon happened.

The same point is : both the video images come from external.

Are they the same issues ?
Do you have the same issues ?

I have been stuck for days.
Need your help, thanks.

Decklink SDK version : 11.4.0
Decklink Card : Decklink mini recorder 4K
Unity version : 2018.2.3.f1
Unity platform : Windows Standalone (In Editor)
Unity Graphic Api : D3D11/D3D12/OpenGLCore/OpenGLES2/OpenGLES3
Cpu : Core i7 6700k
Ram : 32G
Graphic Card : NVIDIA GeForce GTX 1070

The mp4 file: _fileWriter3.mp4 - Google Drive

Does the same issue happen in Windows Standalone builds?

Have you tried profiling it to see if the framerate isn’t actually 60 fps?

I will test it in Windows Standalone builds.
And I am surely 60 fps.
You can download the mp4 file to have a test with VideoPlayer.