0. Please download demo project from this link (If you don't want to download the whole project, you can find CameraController.cs script at the end of this blog post). You can open this project with Unity 5.0 (or newer), press play, and move your camera around with arrow keys (Up, Down, Left, Right), and zoom in (Left Ctrl or Left Mouse button), zoom out (Left Alt or Right Mouse button).
Now, to make a good demo video for your assets, you should:
1. Prepare scene which you want to make video for.
2. Disable your current camera
3. Create a new camera, setup its position, angle... so you can have a nice view. Then add Rigidbody to it (remember to uncheck "Use Gravity"). Then add CameraController.cs script (from my project) to it.
(step 2 and 3: or you can just add Rigidbody & my script to your current camera if you know what you are doing :) )
4. CameraController.cs has 2 parameter: Move Speed and Zoom Speed. I think you know what do them mean. The bigger number, the faster your camera moves. I think "1" is good enough.
5. Now press Play and move around to see if you are happy with it.
6. Once you are happy with result, then build a Executable for PC (Win/ Mac/ Linux, depend on your OS).
7. Now run your Executable that you just created, move your camera around to show your beautiful works, and use some programs to record your screen. My favorite screen record program is OBS. You can find a tutorial about it here. Just a note, about Video Bitrates, I think 9999 is ok (you can use higher number for better quality, but I think 9999 is good enough).
8. Output video will be stored (by default) at your Videos folder (on Windows, it is C:\Users\<yourUserName>\Videos. I'm not sure about Mac or Linux).
Demo Evgenia made a demo video with my code:
Feel free to ask me anything you do not understand clearly.