Examples here use the default settings, see the VidStab readme on GitHub for more advanced instructions.
Here's an example video I made
brew install ffmpeg --with-libvidstab
This won't modify your video or create a new video, but it should create a new file called transform.trf
ffmpeg -i clip.mov -vf vidstabdetect -f null -
ffmpeg -i clip.mov -vf vidstabtransform=smoothing=5:input="transforms.trf" clip-stabilized.mov
This should create a new stabilized video called clip-stabilized.mov
Found on a forum here
ffmpeg -i Clip8.mov -i Clip8-vidstab.mov -filter_complex "[0:v:0]pad=iw*2:ih[bg]; [bg][1:v:0]overlay=w" merged.mov