linux – How can I stream video from a webcam to a file on a Beaglebone Black?

I’m trying to stream some data from a USB webcam to a file on a BeagleBone Black-based device. I’m just trying to test the USB connection, so I don’t care about the output format, and don’t want to re-encode the output since that would load the CPU. The device has no video card, no screen, only a serial console and a USB port. It’s running Debian Jessie (ancient, I know).

I’ve tried ffmpeg -f v4l2 -i /dev/video0 -vcodec copy -t 60 -stats test.raw but ffmpeg returns

(NULL @ 0x878c0) Unable to find a suitable output format for 'test.raw'
test.raw: Invalid argument

The webcam is a logitech V-U0015, and it enumerates as /dev/video0.