0 -i RT0c.mkv -t 00 \     -filter_complex "          color=c=black:s=0000x000 [background];          [0:v] scale=000x000 [left];          [0:v] scale=000x000 [right];          [background][left]       overlay       [background+left];          [background+left][right] overlay=x=000 [vout];           [0:a][0:a] amix [aout]      "  -c:v libx000 -preset veryfast -crf 00 -c:a aac -map "[vout]" -map "[aout]" -y \     -f matroska combined.mkv  