The gstreamer framework provides a plethora of ways to process audio and video. I just figured out that the command gst-launch allows testing audio and video on the command line:
First, to check the available ALSA audio devices:
Now, to read from a microphone and immediately playback on a sound device (adjust the hw ids as necessary):
gst-launch alsasrc device=hw:1,0 ! alsasink device=hw:0,0
Show the live video from a webcam on the monitor:
gst-launch v4l2src ! video/x-raw-rgb,width=800,height=600,framerate=30/1 ! xvimagesink
These are just the very basics. Mixing audio and video and recording is more involved, but gst-launch is a good term to start googling for.