Convert variable input formats to black and white MP4 I am currently using an FFMPEG command like:

ffmpeg -i input.mov -vf scale=1920:1080 output.mp4

to convert varying input format file to a fixed resolution MP4 output file.  One final step I need is to make the output Black and White (the input files will be full color).

I have tried both 
    -pix_fmt gray 
and
    -vf format=gray,format=yuv422p

but both just result in a black output video.

After much trawling of google, it looks like the FFMPEG exe I downloaded (for windows) wasn't compiled with the "-enable-gray" option, but I don't know if this makes any difference and don't know how to obtain a windows FFMPEG with this option enabled (building FFMPEG myself looks like a lot of hard work).
Any advice welcome!  Thanks.

PS I should add that the conversion I'm currently doing and any grayscale conversion could be separate steps if required.
Yes, you do need a ffmpeg build with gray pixel format enabled. You should get your binary from the Windows link at ffmpeg. Download the latest 32-bit static build.

You can check if your build has gray enabled by running 

ffmpeg -pix_fmts | findstr /r gray


It should list an entry for gray. 

And use format=gray in your vf chain and -pix_fmt yuv420p together for broad compatibility.


  The command below is for linux. grep will work as findstr!

ffmpeg -pix_fmts | grep -i gray