How to convert an MKV to AVI with minimal loss

In order to just copy the video and audio bitstream, thus without quality loss:

ffmpeg -i filename.mkv -c:v copy -c:a copy output.avi

If you want FFmpeg to convert video and audio automatically:

ffmpeg -i filename.mkv output.avi

 ffmpeg -i "input.mkv" -f avi -c:v mpeg4 -b:v 4000k -c:a libmp3lame -b:a 320k "converted.avi"

My suggestion: use mpeg4+mp3 in avi container.