bin\ffmpeg.exe -i part1.mp4 -i part2.mp4 -filter_complex "[0:v]scale=1280x720,setdar=1/1; [1:v]scale=1280:720[v2]; [v1][0:a][v2][1:a]concat=n=2:v=1:a=1[outv][outa]" -map "[outv]" -map "[outa]" -c:v libx264 -preset ultrafast -qp 0 output.mkv