> failed with stty: stdin isn't a terminal and a timeout.
How do you know it's a timeout?
Also, I ran `brew test vcs` locally with `at(1)` (for a headless environment). Even with this many errors, the exit status is still zero:
```
==> /usr/local/Cellar/vcs/1.13.2/bin/vcs /tmp/vcs-test-20170505-51377-189gb8b/video.mp4 -n1 -o /tmp/vcs-test-20170505-51377-189gb8b/video.png
stty: 'standard input': Inappropriate ioctl for device
Video Contact Sheet *NIX v1.13.2, (c) 2007-2014 Toni Corvera
Unable to locate DejaVu Sans font. Falling back to helvetica.
Processing /tmp/vcs-test-20170505-51377-189gb8b/video.mp4...
Capturing in range [00:02.00-00:00.00]. Total length: 00:02.00
Composing standard contact sheet...
montage: `/tmp/vcs.sR0jsB/vcs-sEhCAT.png' @ error/montage.c/MontageImageCommand/1775.
convert: improper image header `/tmp/vcs.sR0jsB/vcs-sEhCAT.png' @ error/png.c/ReadPNGImage/4362.
convert: no images defined `/tmp/vcs.sR0jsB/vcs-sEhCAT.png' @ error/convert.c/ConvertImageCommand/3254.
identify: improper image header `/tmp/vcs.sR0jsB/vcs-sEhCAT.png' @ error/png.c/ReadPNGImage/4362.
convert: improper image header `/tmp/vcs.sR0jsB/vcs-sEhCAT.png' @ error/png.c/ReadPNGImage/4362.
convert: no images defined `/tmp/vcs.sR0jsB/vcs-sEhCAT.png' @ error/convert.c/ConvertImageCommand/3254.
Adding header and footer...
identify: improper image header `/tmp/vcs.sR0jsB/vcs-sEhCAT.png' @ error/png.c/ReadPNGImage/4362.
convert: improper image header `/tmp/vcs.sR0jsB/vcs-sEhCAT.png' @ error/png.c/ReadPNGImage/4362.
Output format set from output filename
Done. Output wrote to /tmp/vcs-test-20170505-51377-189gb8b/video.png
Cleaning up...
stty: invalid argument ''
Try 'stty --help' for more information.
```
I know nothing about this `vcs` otherwise, but I think this needs to be resolved one way or another.