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For instance, a popular and powerful app for Android is Open Camera.  But if you are satisfied with the native app, it's probably easiest to stick with that.

Top-Down Video Recording

You can use your mobile device to record top-down video.  This can be handy if you wish to use handwriting, instruments, financial calculators, or even just discuss a photo or image in a book as a mini-lecture.  This may be an essential part of your lecture or demonstration teaching, or it may simply be a creative way to teach with video, instead of using screencasting or filming yourself.  

Gooseneck Arms

Obviously, you'll need a way to support your mobile device (or camera) above your workspace.  You may have audio-video equipment such as scissor arms for supporting microphones (you can get adapters to go between screw-thread sizes) but if not, gooseneck arms, together with mobile phone clips, can be low-cost options:

Here's a small-budget example that's strong enough to support a webcam or mobile phone.  

Here's a more expensive option that can support mirrorless digital cameras, or possibly lightweight DSLR cameras as well.  

Simultaneous or Separate Audio?

With top-down recording (as with screencasting) you have the option of recording your voice while you are recording the video, or recording your voice narrative separately, and attaching it to the video later using editing software. 

Recording simultaneously is obviously faster, although depending on what you are doing, it could be trickier to get a clean, clear narrative.  It's probably best to try simultaneous recording first, and if you find that it's difficult, record the video and narrative separately.

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