ffmpeg and the 'unable to find suitable output' error
You have a lonely -s option there. It misses its argument.
You should specify the size you want or leave it out entirely – otherwise it will not interpret -codec:v correctly and assume mpeg4 is your output filename.
Additionally, use -b:v instead of just -b – it's ambiguous.
ffmpeg -i video.mkv -s 1280x720 -codec:v mpeg4 -bf 1 -b:v 2567k -mbd 2 -g 300 -flags cgop -acodec copy video.avi