ffmpeg \
   -i /Users/Malthe/test//1.mkv \
   -i /Users/Malthe/test//2.mkv \
   -i /Users/Malthe/test//3.mkv \
   -i /Users/Malthe/test//4.mkv \
   -i /Users/Malthe/test//5.mkv \
   -i /Users/Malthe/test//8.mkv \
   -i /Users/Malthe/test//9.mkv \
  -filter_complex " \
      [0:v] setpts=PTS-STARTPTS, scale=qvga [a0]; \
      [1:v] setpts=PTS-STARTPTS, scale=qvga [a1]; \
      [2:v] setpts=PTS-STARTPTS, scale=qvga [a2]; \
      [3:v] setpts=PTS-STARTPTS, scale=qvga [a3]; \
      [4:v] setpts=PTS-STARTPTS, scale=qvga [a4]; \
      [5:v] setpts=PTS-STARTPTS, scale=qvga [a5]; \
      [6:v] setpts=PTS-STARTPTS, scale=qvga [a6]; \
      [a0][a1][a2][a3][a4][a5][a6]xstack=inputs=7:layout=0_0|w0_0|w0+w1_0|0_h0|w0_h0|w0+w1_h0|0_h0+h1[out] \
      " \
    -map "[out]" \
      -c:v libx264 -preset slow -crf 0 -c:a copy output.mkv