For example, let’s say that I want to record a turntable of a 3D model in UE, then use the clip on top of some background in video editing app. Is it even possible?.. Maybe from Sequencer with some custom depth info?
Okay,
At this time UE not able to give that you directly; But I have Solution For this…,
You Just Want TurnTable Right…,
Use A flat Background Like Matt Pass while You render Your Model.
Then You Can Seperate That Colour as for alpha Using Foundry Nuke Or Adobe After Effect. You can also do This in Photoshop CC.
It is simple process like Rotoscopy for excrate mask or Alpha.
That’s a good idea, I’ll try that. So basically a green screen inside UE to key it out in video app 
Thanks!
Or delete all lighting (everything black), disable bloom, use fully white skybox. A b/w mask
You are Wellcome…,
That Can Also Be Solution … You Give Me another Idea Thanks…
Plz tell me How to create white skybox. I am new in unreal engine.
for recording with transparency export from Sequencer/MRQ as exr or png sequence with alpha enabled — mp4 cant carry it. if you want to then re-import and overlay that result in engine (like preview before editing), you need something that plays the alpha back correctly. mp4/h264 will lose it again. i use alpha video player from fab Alpha Video Player - Transparent Video UMG Widget & UI Media Component (UE5) | Fab for that — it replays the exr/png sequence or a prores 4444 with alpha as a UMG widget with proper compositing, so you can check the turntable loop in engine before you composite in ae