Sending video to Android Camera
For testing, depending on your app you have a few choices:
If the the app just needs camera and is configurable either:
a) use the Android emulator on PC which can take a USB webcam as input and use that to inject the images/video feed.
b) Android devices starting with Android 9 can accept external USB Camera and use the standard API or need custom libraries for earlier version of Android. This would require the app to support such alternate inputs.
If you are testing biometric, there is a way to test with fingerprint using emulator but on physical hardware per the documentation secure camera hardware is required to prevent injection attacks on face authentication.