I had been using:
ffmpeg -pass 1 -passlogfile ffmpeg2pass -g 1 -b 16000k -i input.mov output.wmv
ffmpeg -pass 2 -passlogfile ffmpeg2pass -g 1 -b 16000k -i input.mov output.wmv
which at one point gave me an error on the second pass:
[msmpeg4 @ 0x7fde41844e00] requested bitrate is too low
I tried increasing 16000k to 32000k, but this did not make the error go away. Turns out I just needed to switch the order of the parameters:
ffmpeg -pass 1 -passlogfile ffmpeg2pass -g 1 -i input.mov -b 16000k output.wmv
ffmpeg -pass 2 -passlogfile ffmpeg2pass -g 1 -i input.mov -b 16000k output.wmv