For small screen captures I find it most convenient (and free) to use the brilliant Cam Studio. I set “region” to fixed and in this case, fix the left corner in place too. Recording to MP4 is efficient, but still requires trans-coding with Handbrake anyway to use common codecs that most devices understand (despite the MP4 licencing issues). It’s cleaner and no bother, for short, small videos, to record to AVI, and then trans-code with Handbrake. It also permits the additional step, if required, of trimming the AVI with the venerable but indispensable Virtual Dub.