DirectShow

Ffmpeg can take input from "directshow" devices on your windows computer. These are typically video or audio devices that are attached.

c:\> ffmpeg -list_devices true -f dshow -i dummy
ffmpeg version N-45279-g6b86dd5... --enable-runtime-cpudetect
  libavutil      51. 74.100 / 51. 74.100
  libavcodec     54. 65.100 / 54. 65.100
  libavformat    54. 31.100 / 54. 31.100
  libavdevice    54.  3.100 / 54.  3.100
  libavfilter     3. 19.102 /  3. 19.102
  libswscale      2.  1.101 /  2.  1.101
  libswresample   0. 16.100 /  0. 16.100
[dshow @ 03ACF580] DirectShow video devices
[dshow @ 03ACF580]  "Integrated Camera"
[dshow @ 03ACF580]  "screen-capture-recorder"
[dshow @ 03ACF580] DirectShow audio devices
[dshow @ 03ACF580]  "Internal Microphone (Conexant 2"
[dshow @ 03ACF580]  "virtual-audio-capturer"
dummy: Immediate exit requested

Then use the listed devices like

c:\> ffmpeg -f dshow -i video="Integrated Camera" out.mp4