bin\ffmpeg.exe -i part1.mp4 -i part2.mp4 -i part3.mp4 -filter_complex "[0:v]scale=-1:720,pad=1280:720:(1280-iw)/2:0[v1];[1:v]scale=1280:720[v2];[2:v]scale=-1:720,pad=1280:720:(1280-iw)/2:0[v3];[v1][0:a][v2][1:a][v3][2:a]concat=n=3:v=1:a=1[outv][outa]" -map "[outv]" -map "[outa]" -c:v libx264 -preset ultrafast -qp 0 output.mkv

[Parsed_concat_5 @ 02924a00] Input link in2:v0 parameters (size 1280x720, SAR 54
00:5401) do not match the corresponding output link in0:v0 parameters (1280x720,
 SAR 1:1)
[Parsed_concat_5 @ 02924a00] Failed to configure output pad on Parsed_concat_5