Pix format errors when piping

[rvn-dev]

Have glc-capture/play working fine.
If you don't have glxgears sudo apt install mesa-utils
Copied scripts/pipe_ffmpeg.sh to a new dir and tried
glc-capture --start --pipe=pipe_ffmpeg.sh glxgears
and it gives following error

Running synchronized to the vertical refresh.  The framerate should be
approximately the same as the monitor refresh rate.
[   0.10s       pipe error ] unsupported pixel format: YV12_420
[   0.10s glc_thread error ] Invalid argument (22)
[   0.10s       pipe error ] Invalid argument (22)
282 frames in 5.0 seconds = 56.396 FPS

Not saving off a file in the folder, probably because of pixel format issue. This is on ubuntu 16.04 and ffmpeg 2.8.15 built from glcs master. Do you have any idea how to resolve?